"There's not much left to be resolved," Senate Finance Committee Chairman Charles Grassley, R-Iowa, said Thursday after a House-Senate meeting. "The staff is going to work real hard over the Fourth of July break."

The two chambers passed their respective bills in late 2005, and talks on a compromise have dragged on since March.

At the prodding of House Speaker Dennis Hastert, R-Ill., and Senate Majority Leader Bill Frist, R-Tenn., negotiators have been meeting almost daily in recent weeks. But progress has been incremental.

"Days and days and days of the same ditto," House Majority Leader John Boehner, R-Ohio, a chief sponsor of the House bill, said as he emerged from one recent meeting.

Lynn Dudley, vice president of the American Benefits Council, which represents companies with pension plans, said her organization is not overly concerned by the missed deadlines.

"The truth of the matter is they've got to get this thing right. It's the bedrock of retirement security for millions of people," she said.

The toughest issue has been working out a definition of an "at risk" company that would be required by the bill to increase contributions to its pension plan.

Currently, company pension plans are underfunded by an estimated total of $450 billion. The Pension Benefit Guaranty Corp. — the federal agency that insures private pension plans much like the Federal Deposit Insurance Corp. insures bank accounts — estimates that $100 billion of that is with companies with serious funding problems.

The Pension Benefit Guaranty Corp., which is self-funded from premiums, is itself burdened by a $22.8 billion deficit because it has had to take over the benefits obligations of companies that go bankrupt and terminate their plans.

Without a fix, many fear the whole defined benefit pension system could implode in a repeat of the late 1980s savings and loan crisis that ended up requiring a $130 billion taxpayer bailout.

The original Senate bill would have linked at-risk status to a company's credit rating, an idea strongly opposed by General Motors and others in the auto industry with poor credit status.

Negotiators have since backed off this approach, but industry sources have expressed concern that other proposals also are overly harsh — such as defining plans that are less than 80 percent funded as at risk for default.

One sticking point is whether credit balances, extra contributions paid into a plan to cover future years, should be counted as an asset when determining a plan's financial viability.

Former Michigan Gov. John Engler, who is now president of the National Association of Manufacturers, said excessively tough rules could be counterproductive. "The cost goes up if somebody terminates a plan and then turns it back over to the pension board," he said.