With one eye on the clock, congressional negotiators labored Thursday to settle disputes standing in the way of agreement on the most sweeping changes to the pension system in years.

House Majority Leader John Boehner, R-Ohio, said there continued to be a House-Senate split on whether to attach a package of popular federal tax breaks to the pension bill. Senate negotiators want it on the bill, while House GOP leaders prefer a separate tax bill linking the tax breaks to an estate tax cut that the Senate has rejected on several occasions.

House and Senate staffers worked through the night to draft language on the pension bill that would restructure, and ideally restore financial integrity to, traditional employer-based pension plans.

Lawmakers were reviewing that language Thursday, acknowledging that they would have to reach an agreement during the day if the House is to pass the bill before its planned departure Friday for the month-long August recess. The Senate will be in session one more week.

The bill, years in the making and under negotiation for five months, has the goal of strengthening traditional employer-based pension plans, crucial to the retirements of some 44 million Americans. It would also provide for steps, such as automatic enrollment, to ensure that 401(k) plans and IRAs, increasingly the main savings option of younger workers, are utilized by more people.

The bill would require all defined-benefit plans to reach full funding within seven years, presumably shrinking the current level of underfunding estimated at $450 billion. Companies that are seriously underfunded would be required to make extra payments to catch up with their contributions.

The legislation also attempts to protect the fiscal integrity of the Pension Benefit Guaranty Corp., the federal agency that insures pension plans and takes over plans abandoned by companies. The PBGC, running a deficit of $22.8 billion, has so far operated on premiums and interest earnings, but there is concern that it could require a taxpayer bailout if more major employers dump their pension plans.

Negotiators said late Wednesday that there were still three major outstanding issues, including whether to include the tax breaks.

The original Senate bill passed last year gave financially struggling airlines, specifically Northwest Airlines Corp. and Delta Air Lines, up to 20 extra years to reach full funding. Other airlines would also receive breaks in their repayment schedules.

The House demanded less generous breaks for the airlines, and it appeared that Northwest and Delta would end up with a grace period of about 10 years. But Sen. Mike Enzi, R-Wyo., chairman of the Health Education, Labor and Pensions Committee, said lawmakers still want to look at the final language being drafted before signing off on the compromise.

Negotiators Thursday were also looking over language dealing with an enduring dispute over who is permitted to offer investment advice on retirement plans.

Boehner, a chief negotiator, has pushed a plan that would give financial firms the authority to provide investment advice on 401(k) and IRA plans. But he has met resistance in the Senate because of concerns that firms that managed plans would have conflict of interest problems in offering advice.

"The people who can give the best advice also happen to sell products," Boehner said at an earlier news conference. Under current law such financial firms can't advise investors, he said. But "I believe there is a way that protects the interest of the recipients while at the same time allows advice to get into their hands," Boehner said.

Under a proposal circulated by the House side, employers with retirement plans would be responsible for selecting and reviewing advice providers. Fiduciaries for employer-sponsored plans such as 401(k)s that provide advice must base their recommendations on a computer model that is certified and audited by an independent party.