The federal agency that insures the private pensions of 44 million workers said Tuesday that its deficit was $22.8 billion in 2005, as big airlines in bankruptcy dumped their pension liabilities.

The Pension Benefit Guaranty Corp. disclosed in its annual financial report that as of Sept. 30, it had $56.5 billion in assets to cover $79.2 billion in pension liabilities.

There has been an explosion in recent years in the number of big, ailing companies -- especially in labor-heavy industries like airlines and steel -- transferring their pension liabilities to the PBGC. With billions of dollars flying out of the agency's door, concern has been mounting in Congress and elsewhere over its financial footing.

The PBGC's $22.8 billion deficit for fiscal 2005 is slightly narrowed from the $23.3 billion shortfall it reported a year ago, which was a record. If other liabilities it assumed after the end of the fiscal year on Sept. 30 had been counted, the 2005 deficit would have been $25.7 billion, the agency said.

Without a legislative overhaul of the private pension system, the PBGC eventually will run out of money to pay the pension claims of the retirees of companies whose plans it has assumed, some experts predict. That would mean that people retiring from financially troubled companies would have nowhere else to turn for their promised pension payments -- raising the possibility of a taxpayer bailout.

Traditional employer-paid pension plans, giving retirees a fixed monthly amount based on salary and years of employment, are now estimated to be underfunded by as much as $450 billion. That could jeopardize the retirement security of millions of Americans, lawmakers have warned.

United Airlines and US Airways used bankruptcy earlier this year, with judges' blessings, to slash costs by dumping their employee pension liabilities -- a combined $9.6 billion -- onto the PBGC.

Delta Airlines and Northwest Airlines, which both filed for Chapter 11 bankruptcy protection on Sept. 14, may seek to do the same. The pension plans of Delta and Northwest, the nation's No. 3 and No. 4 airlines, are underfunded by an estimated $16.3 billion.

And there is speculation that auto parts maker Delphi Corp., which filed for protection from creditors last month, also could terminate its pension plan and transfer liability to the federal agency.

For months, lawmakers have been grappling with an overhaul of the rules governing company pension plans to tighten controls over employers with underfunded plans and shore up the PBGC's finances. Legislation cleared a key House committee last Wednesday, advancing what could be the most important retirement issue Congress will address this year as Social Security's overhaul has faded into the background.

The full House could take up the bill as early as this week.

Democrats generally oppose it. They say it could lead some employers to drop their pension plans or switch from traditional so-called defined-benefit plans to less expensive defined-contribution programs, such as 401(k) plans -- in which employers contribute to a retirement fund and workers receive only what the investments have earned.

Many companies are replacing defined-benefit pension plans with defined-contribution plans. The PBGC only backs defined-benefit plans, which are most prevalent in older industries such as automobile manufacturing, steel and airlines -- now reeling from record fuel costs, historically low fares and cutthroat competition.

The agency was created in 1974 as a government insurance program for traditional employer-paid pension plans. Companies pay insurance premiums to the agency, and if an employer can no longer support its pension plan, the agency takes over the assets and liabilities and pays promised benefits to retirees up to certain limits.

Employees do not receive their full pension benefits when the PBGC takes over a plan. The maximum annual benefit for plans assumed by the agency this year is $45,614 for workers who wait until 65 to retire.