Washington ? President Barack Obama and top congressional Democrats closed in on agreement Friday on cost and coverage issues at the heart of sweeping health care legislation, their marathon White House bargaining sessions given fresh urgency by an unpredictable Massachusetts Senate race.

Negotiators are “pretty close,” Senate Majority Leader Harry Reid said after returning to the Capitol in late afternoon.

A White House statement said there are “no final agreements and no overall package.” But no further meetings were scheduled, and Rep. Jim Clyburn, D-S.C., the third-ranking House Democrat, said, “Something should be going to CBO very soon,” indicating that aides were drafting the decisions made around the table in the White House Cabinet Room. The Congressional Budget Office is the official arbiter of the cost and extent of coverage that any legislation would provide.

No details were immediately available, and congressional aides stressed the decisions made at the White House had not yet been fully shared with the Democratic rank and file.

One key obstacle appeared on its way to a resolution when Sen. Ben Nelson, D-Neb., requested the elimination of an intensely controversial, one-of-a-kind federal subsidy to cover the entire cost of a Medicaid expansion in his home state.

That provision in the Senate-passed measure has drawn criticism from governors and others in both political parties from the moment it was disclosed, and even former President Bill Clinton urged that it be jettisoned. “That Nebraska thing is really hurting us,” he told House Democrats in an appearance designed to build support for the overall legislation.

In its place, officials said Obama and lawmakers decided to increase federal money for Medicaid in all 50 states, although it was not clear if there would be enough to cover the expansion completely.

The increase in the Medicaid program is a key element in the bill’s overall goal of expanding health coverage to millions who lack it. The bill also envisions creation of new insurance exchanges, essentially federally regulated marketplaces where consumers can shop for coverage. Individuals and families at lower incomes would receive federal subsidies to defray the cost.

The overhaul legislation also is designed to curb insurance industry practices such as denial of coverage on the basis of pre-existing medical conditions, an issue that Obama stressed in a closed-door appearance before the House rank and file. The measure will be a “patients’ bill of rights on steroids,” he said, according to officials who disclosed his comment on condition of anonymity because the setting was private.

At the White House, spokesman Robert Gibbs was unequivocal that Obama’s yearlong campaign for health care legislation would prove successful. “As you heard the president say yesterday, we’re going to get health care done,” he said.

Not everyone was quite so certain, particularly given poll results from Massachusetts that showed Republican Scott Brown within reach of a possible upset over Democrat Martha Coakley in a three-way race to succeed the late Sen. Edward M. Kennedy.

“If Scott Brown wins, it’ll kill the health bill,” said Rep. Barney Frank, D-Mass, reflecting that the Republican would provide opponents of the health care bill a decisive 41st vote to uphold a filibuster and block passage. Frank predicted Coakley would ultimately win the seat and thus preserve the 60-vote Senate majority essential to pass the legislation, and Obama hurriedly scheduled a weekend campaign trip to the state.