United Airlines, which appears likely to default on its pension plans in the coming months, invested a larger-than-average share of its $6.6 billion pension portfolio in illiquid investments, while also investing liberally in junk bonds, technology and pharmaceutical start-ups, even a gold mining company in Ghana.

But a rare look at the latest available detailed information on the contents of United's pension fund, as of December 2002, shows no extraordinary missteps or unique failures of judgment; the airline got into trouble more or less the way virtually every other pension fund did that year.

While United's investment results were not far out of step with other pension funds, the losses had a far more devastating effect on the fund because they coincided with United's own business troubles. Cash-rich companies that suffered pension losses during the bear market have been able to pump new money into their plans. But United, a unit of the UAL Corporation, is in bankruptcy, and it has no spare cash with which to replace the pension money lost in the stock market.

The market's rebound since then has not helped United much either. Even though the value of its pension assets has gone back up, its obligations have grown, too. Its pension fund finished 2003 with $6.9 billion in assets, or just 53 percent of the amount needed to pay its $13.1 billion of obligations to retirees.

United's difficulties with its pension plans are prompting some specialists to call for a re-examination of the way all companies handle their pension investments, which they say forces the government to act as a backstop for speculative investments over which it has little oversight. When a company pension fund fails, the government's pension insurance agency, the Pension Benefit Guaranty Corporation, makes up the losses.

Rich Nelson, a spokesman for United, said that if anything, the airline's pension investments surpassed industry benchmarks.

"The return on United's current pension program since its inception 17 years ago is in line with, and slightly ahead of, comparable large corporate plans," Mr. Nelson said. United has four separate pension plans for different groups of employees, but keeps the assets pooled in a single trust.

Like most corporate pension funds, United's favored stocks above all else. It held about 61 percent of its total assets in stocks at the end of 2002, with about one-fifth of those the stocks of foreign businesses. The average corporate pension fund was about the same.

As a stock picker, United fell prey to many of the same highflying dot-coms and telecom flameouts that brought grief to investors everywhere when the technology bubble burst. Its pension fund also had a sizable exposure to the energy-trading companies - like El Paso Energy, Dynegy and the Williams Companies - that became embroiled in accounting disputes that year. The biggest energy-trading disaster, Enron, does not appear on the list, however.

United's pension investments also included companies found well off the beaten path, in emerging countries like Russia, Thailand, China and Panama. Some of these - like the Ghanaian gold mining concern - were gambles that paid off. Others, like a $5 million bet on an Israeli software company, Check Point Software Technologies, were losers that ended 2002 worth just a fraction of what United paid for them.

The most telling sign of United's stomach for risk was its pension fund's relatively large position in stocks that are not publicly traded. United had about 5.1 percent of its pension assets in these stocks, known as private equities - not enough to be the ruination of the pension fund, but still well above the average, just 3.4 percent, for the company pension funds tracked by Greenwich Associates, a research and consulting firm.

Some pension watchdogs frown on the use of private equities because they are hard to sell. They are normally offered through investment partnerships that require commitments of 8 to 10 years, and they are very difficult to cash out of without losses. Their year-to-year performance is hard to evaluate because there are no uniform disclosure requirements and they have no agreed-upon market price.

At the end of 2002, United's commitments had not yet borne fruit. It paid $403.5 million for the private equities but said they were worth just $313.4 million at that point.

Mr. Nelson called the airline's position in private equities "an appropriate level, in keeping with our overall diversification strategy."

Over all, the value of United's pension assets fell by about 9.3 percent in 2002, according to separate records filed with the Securities and Exchange Commission. That compares to a 0.2 percent average decline in pension asset values that year, according to Greenwich Associates. (Both year-to-year changes include the effect of company contributions and payments to retirees during the year, as well as investment returns.)

Virtually all companies that operate pension funds have ranged far afield from the conservative bonds that secured pensions years ago. Today, the typical pension fund has about 60 percent of its assets in stocks and about 30 percent in bonds, and the rest in what are known as alternative investments: private equities, real estate, high-yield bonds, even hedge funds.

The goal in investing so aggressively has been to reduce compensation costs and bolster profits. The accounting rules for pension funds help, by allowing companies to project the long-term gains they expect from their pension investments, then factor that projection into their bottom lines - even in years when the projections are dead wrong.

United assumed that its pension fund would earn 9.75 percent in 2002, for instance, and used that assumption to reduce its reported labor costs, even though the pension fund actually lost money.

This feature of the accounting rules has drawn much criticism from investors, who find it misleading. Pension specialists fault it further, saying it has become a powerful incentive for companies to invest in riskier assets. The greater the risk, the higher the projected returns a company can justify, and the stronger the kick to the bottom line.

"The accounting encourages a mismatch, because they get an earnings windfall," said Zvi Bodie, a finance professor at Boston University who has warned for years of the dangers of trying to secure pension promises with stocks and other volatile investments. "It's bad for employees because it increases the chance that they won't get their promised benefits. It's bad for the P.B.G.C. It's bad for the taxpayers. So who's it good for? It's good for the firms that manage the equities."

Despite such warnings, many pension officials say today's approach to pension investing is sound. Stocks, they say, can be expected to yield higher returns over the long term, which is why they believe they make sense given the nature of pension commitments far into the future.

"The company's investment strategy,'' Mr. Nelson, United's spokesman, said, "emphasizes diversification among asset classes, such as equity and fixed income, diversification among investment strategies such as growth stocks and value stocks, and diversification among the managers. The strategy focuses on long-term returns, given the plans' long-term liabilities."

United's list of pension investments is not routinely open to public scrutiny, although it is not officially secret either. A copy of its list was provided to The New York Times by a government official after numerous requests.

One of United's more venturesome investments was a stake in Ashanti Goldfields, a large mining company that went public in 1994, when the government of Ghana sold off more than 100 state enterprises. Though some critics deplored what they called the sale of "Ghanaians' birthright" at the time, the stock offering was widely hailed as a success, with development economists calling it a sign that long-overlooked Ghana was ripe for foreign investment. In 1999, Ashanti became the first African operating company to trade on the New York Stock Exchange.

Ashanti's stock price went nowhere in the late 1990's, but then rocketed in 2002, when two other big mining companies, one in London and the other in South Africa, mounted a billion-dollar bidding war for Ashanti's stock.

Last April the South African company finally won, and Ashanti Goldfields was merged into AngloGold in a deal with a reported value of $1.3 billion. United's pension list foreshadows this success, stating the pension fund had paid $147,000 for stock worth $310,000 at the end of 2002. The airline was unable yesterday to describe what happened to its investment after that.

But United's investments in private equities were less auspicious. In 1996, for example, United made a commitment to a private investment partnership being offered by Willis Stein & Partners, an investment firm in Chicago, where the airline has its headquarters. Willis Stein said it would put its investors' money to work buying and building up midsize companies in the Midwest, and by 1998 it was reporting returns in the 40 percent range.

Willis Stein then offered a second partnership and United made a commitment to that one, too. But that partnership bought, among other things, a Chicago publishing company that focused on technology titles, which was caught up in the technology crash. At the end of 2002, United's list showed a current value of $9 million for the second partnership, and a historical cost of $23 million.

Regulators have watched companies make pension investments like these with growing concern in recent years, knowing the federal pension agency would be called upon to cover the losses if the markets soured. But pension regulators have little power to influence such investment decisions. The pension funding rules provide detailed instructions for how much companies must put into their pension funds, but they say almost nothing about how the money should then be invested.

As more and more failed pension funds have gone to the pension agency in recent years, some officials have proposed new measures to discourage excessive risk-taking. One idea being considered is to change the premiums the government charges for its pension insurance.

Currently, the agency charges most companies flat-rate premiums, $19 per covered employee, no matter how risky or safe the assets in the pension fund. Proponents of the change say that if the premiums were tied to risk, not only would the deficit-ridden pension agency get more revenue, but companies would have an incentive to rein in the riskiness of their pension investments.

"It certainly would not be hard to do this for a private insurance entity," Mr. Bodie said. But the pension agency would have to get Congressional approval, he said.