Congress should tighten and clarify rules requiring employers to fund traditional pension plans, and it should compel companies to tell workers the true financial condition of their plans, the head of Congress's Government Accountability Office told a Senate panel yesterday.

Rules allow companies to use different methods to compute a plan's status, resulting in "inconsistent, confusing and competing numbers that increase the risk" that workers and regulators will fail to grasp that a plan is in trouble before it is too late, U.S. Comptroller General David M. Walker told a hearing of the Senate Finance Committee.

The head of the government's troubled pension insurance agency, the Pension Benefit Guaranty Corp., and the director of the Congressional Budget Office also called for tighter rules.

The hearing was one of several on Capitol Hill this week as lawmakers seek ways to shore up the PBGC and the plans it insures without driving companies with healthy pensions out of the system.

But the difficulties involved in this effort were immediately underscored by the appearance of the chief executives of Northwest Airlines Corp. and Delta Air Lines Inc. and representatives of several of their unions. Those officials pleaded with the senators to approve a measure sponsored by Sens. John D. Rockefeller IV (D-W. Va.) and Johnny Isakson (R-Ga.) that would allow troubled airlines to stretch out required payments to their pension plans while freezing benefits and shifting to a less-expensive 401(k)-type retirement plan.

If that is not allowed, Northwest chief executive Douglas M. Steenland and Delta chief executive Gerald Grinstein warned the panel, their airlines and probably other "legacy" carriers would follow United Airlines' UAL Corp. and US Airways Group Inc. into bankruptcy protection, which would allow them to shift their pension plans to the PBGC.

That agency has already taken on billions in unfunded pension liabilities in recent years, much of it from the airline and steel industries. Under existing rules, parent companies of many of those plans, including United, were required to put little or no cash into them even as they teetered on insolvency.

Further, underfunding among 1,108 plans that are each short by at least $50 million totaled $353.7 billion at the end of last year, PBGC Executive Director Bradley D. Belt said. And total underfunding in the traditional pension system may be as high as $450 billion, he said.

The Bush administration has proposed a program that not only would tighten rules but also would raise insurance premiums that operators of traditional pensions must pay to the PBGC. It also would sharply boost premiums for employers that are themselves financially shaky.

CBO Director Douglas J. Holtz-Eakin said it is logical to require pension operators to choose between funding their plans adequately or paying higher insurance premiums.

But employers, especially those with well-funded plans, oppose premium increases.

The proposal would boost premiums required of well-funded plans from $19 per participant to $30 and index it to inflation. Belt said the PBGC gets $600 million annually from this premium, and the administration proposal would raise that total to $900 million.