(Updates throughout with additional details)

WASHINGTON -(Dow Jones)- House Democratic leaders on Friday worked to resolve complaints within their ranks on health-care legislation, with President Barack Obama set to make an appeal to Democratic lawmakers on the eve of a scheduled Sunday vote.

A vote on the $940 billion legislation is expected Sunday. Four Democrats who voted against a version of the bill last November--Reps. John Boccieri, (D., Ohio) and Allen Boyd, (D., Fla.), Scott Murphy (D., N.Y.) and Suzanne Kosmas (D., Fla.)--announced that they would vote in favor of the most current legislation.

Their announcements are positive signs for Democratic leaders, who have seen several new commitments to the bill this week. Democrats' efforts were also boosted by endorsements of the legislation's passage by the AARP, the nation's leading seniors' group, and the American Medical Association, the nation's leading doctors' group.

President Barack Obama, who has taken a very active role this week in courting undecided lawmakers to vote for the bill, will speak to House Democrats. The House Rules Committee also will meet Sunday to vote on the structure of Sunday's formal debate on the House floor on the measure.

House Majority Leader Steny Hoyer, (D., Md.) told reporters Friday that "we're going to have the votes...when the roll is called." House Speaker Nancy Pelosi, (D., Calif.) reiterated the remarks, saying, "When we bring the bill to the floor, we will have a significant victory for the American people."

But they face challenges as well. They are still seeking to woo antiabortion Democrats, as well as other lawmakers concerned about issues ranging from Medicare reimbursements to the affordability of insurance coverage under the bill.

Pelosi met late Friday with members of the Congressional Pro-Choice Caucus, as she sought a way to navigate divisions within her caucus on the abortion issues. Antiabortion Democrats--whose votes may be needed to win passage of the legislation--are seeking a vote on more restrictive language barring funding of abortion through subsidies that the bill would provide to pay for insurance coverage.

In order to pass the legislation, Democratic leaders are using a parliamentary tactic called budget reconciliation--a procedure that doesn't allow for changes to the bill that don't have an effect on the federal budget. Because of that, any changes to the bill related to abortion likely would be ruled out by the Senate parliamentarian once the measure came to the Senate for a vote.

Pelosi did not close the door on making possible changes to other parts of the bill, saying that there would be a "manager's amendment" to the bill. She said the amendment "will be brief" and will not "address too many issues."

Pelosi acknowledged concerns by Rep. Peter DeFazio, (D., Ore.) that the current bill does not adequately pay doctors and hospitals in some areas for treating Medicare patients. Lawmakers from midwest and northwest areas, such as DeFazio, say their districts have been shortchanged for years under Medicare.

"We're working on that language," Pelosi said.

Rep. Stephen Lynch, (D., Mass.), who unexpectedly said this week that he planned to vote against the bill, made his opposition official Friday afternoon. Despite personal appeals from President Barack Obama and Vicki Kennedy, the wife of the late Sen. Edward Kennedy, Lynch said he will remain a firm "no" vote on the bill.

Lynch said he does not trust that the Senate, which often lacks the votes to pass legislation from the House, will be able to pass the measure under reconciliation.

"My concern is that these other bills will become one more bill on the pile," Lynch said.

Business groups continued to criticize the measure Friday. The National Association of Manufacturers is urging the House to vote against the health-care overhaul, arguing that it would unfairly burden manufacturers by raising costs and destroying jobs.

The Retail Industry Leaders Association also urged the House to vote against health-care legislation, saying it prohibits retailers from designing and offering health benefits that they deem best for their employees. RILA, a trade group that represents major retailers, includes companies such as Wal-Mart Stores Inc. (WMT), Target Corp. (TGT) and Best Buy Co. (BBY).

(Shayndi Raice contributed to this report.)

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