WASHINGTON — One by one, House Democratic fence-sitters began choosing sides Friday, and the long, turbulent struggle over landmark health care legislation tilted unmistakably in President Barack Obama’s direction.

In full campaign mode, his voice rising, the president all but claimed victory, declaring to a cheering audience in Virginia, “We are going to fix health care in America.”

With the showdown vote set for Sunday in the House, Obama decided to make one final, personal appeal to rank-and-file Democrats, arranging a Saturday visit to the Capitol. Republicans, unanimous in opposition to the bill, complained anew about its cost and reach.

Under a complex — and controversial — procedure the Democrats have devised, a single vote probably will be held to send one bill to Obama for his signature and to ship a second, fix-it measure to the Senate for final passage in the next several days.

Democratic leaders and Obama focused last-minute lobbying efforts on two groups of Democrats, 37 who voted against an earlier bill in the House and 40 who voted for it only after first making sure it would include strict abortion limits that now have been modified.

Reps. John Boccieri of Ohio, Scott Murphy of New York and Allen Boyd and Suzanne Kosmas of Florida became the latest Democrats to announce support for the bill after voting against an earlier version that passed, bringing the number of switches in favor of the bill to seven.

On the other side of the ledger, Rep. Michael Arcuri of New York and Stephen Lynch of Massachusetts became the first Democratic former supporters to announce their intention to oppose the bill. Lynch said he did so despite a telephoned appeal from Vicki Kennedy, whose late husband, Sen. Edward M. Kennedy, championed health care for decades.

Rep. Anh Cao of Louisiana, the only Republican to support the earlier measure, has also announced his opposition.

The historic legislation, affecting virtually every American and more than a year in the making, would extend coverage to an estimated 32 million Americans who lack it, forbid insurers to deny coverage on the basis of pre-existing medical conditions and cut federal deficits by an estimated $138 billion over a decade.

Congressional analysts estimate the cost of the two bills combined would be $940 billion over a decade.

For the first time, most Americans would be required to purchase insurance, and they would face penalties if they refused. Billions of dollars would be set aside for subsidies to help families at incomes of up to $88,000 a year afford the cost. And the legislation also provides for an expansion of Medicaid that would give government-paid health care to millions of the poor.

Republicans resorted to unusually personal criticism in their struggle against the bill, calling Kosmas a “space cadet” after she announced her position and labeling Pennsylvania Rep. Jason Altmire a “drama queen” for waiting to announce his opposition.

They also suggested the administration had adjusted water allotments to an agricultural region of California to secure the support of two lawmakers but offered no evidence of any link between the two events. Democrats disputed the charge.

In addition, they sought to tarnish Democratic claims of deficit savings, circulating a Congressional Budget Office estimate that deficits would rise by $59 billion once the costs of raising doctor fees under Medicare were added in. The House has already approved the increase in fees, and the bill is awaiting action in the Senate.

Apart from Lynch, several lawmakers who supported the earlier version after the strict abortion limits were incorporated announced they would vote in favor of the new bill. And there was talk among others of finding a largely symbolic way that would allow them to follow. Rep. Marcy Kaptur of Ohio said in an interview she would support the bill if Democratic leaders would first allow a stand-alone vote on tougher abortion restrictions, even though that vote evidently would not affect the health care measure itself.

The political ramifications remained to be fought out in November.

Arcuri’s announcement of opposition reaped a threat from his former allies at the Service Employees International Union, which vowed to try to unseat him in this fall’s Democratic primary in favor of “someone who shares our progressive values.”

Boccieri’s decision to support the bill drew a tart response from the House Republican campaign committee, which issued a warning — “Ohio Dem Uses Press Conference to Announce End of Stint in Congress” — that predicted the first-term lawmaker’s political demise.

One day after Democrats released 153 pages of revisions to their bill, they were back at it, responding to fresh concerns from some of the rank and file about disparities in payment levels to Medicare providers in different areas of the country.

“I’m a ’no’ unless they fix it,” said Rep. Peter DeFazio, D-Ore. “We spent months working this out. If we don’t get it in this bill, we will never get it.” Speaker Nancy Pelosi, D-Calif., said changes were in the works.

Republicans said, as they have from the outset, that Democrats were angling for a government takeover of health care. They also said the cost of the bill would be covered by $900 billion in higher taxes and cuts in future Medicare payments.

The Republicans circulated a letter from Caterpillar Vice President Gregory S. Foley to House leaders, warning that passage of the legislation would raise the company’s health care costs by “more than 320 percent (over $100 million) in the first year alone and put at risk the coverage our current employees and retirees receive.”

The insurance industry said the latest Democratic legislation would decimate a private alternative to traditional Medicare that counts 10 million subscribers. It will “end Medicare Advantage as we know it,” said Robert Zirkelbach, a spokesman for American Health Insurance Plans.” He said Democrats were cutting $200 billion over a decade in projected federal subsidies, and he predicted premiums for seniors would rise as a result.

The government subsidizes private plans at a higher rate than traditional Medicare, and the cuts are aimed at reducing the difference.