The online survey showed increased backing from Republicans and, crucially, the political independents whose support will be essential to winning the November 6 presidential election.

Thirty-eight percent of independents support the healthcare overhaul in the poll conducted after the court ruled Thursday the law was constitutional. That was up from 27 percent from a Reuters/Ipsos poll taken days before the justices' ruling.

Among all registered voters, support for the law rose to 48 percent, from 43 percent before the court decision.

"This is a win for Obama. This is his bill. There's not really any doubt in people's minds, that it belongs to him," said Julia Clark, vice president a Ipsos Public Affairs. "It's his baby. It's literally been labeled Obamacare ... which maybe it works in his favor now that there's a little bit of a victory dance going on."

Republican opposition to the law stayed strong, if somewhat weaker than before the High Court ruled. Eighty-one percent of Republicans opposed it in the most recent survey, down from 86 percent in the poll conducted June 19-23.

Underscoring the intense polarization on the issue, three-quarters of Democrats backed the bill, the same as a week earlier.

FANNING OPPOSITION'S FLAME

In some good news for Republicans, the Supreme Court ruling is energizing opposition to the 2010 healthcare overhaul.

In the new poll, more than half of all registered voters - 53 percent - said they were more likely to vote for their member of Congress if he were running on a platform of repealing the law, up from 46 percent before the ruling.

"This is galvanizing both sides," Clark said.

Obama's Republican challenger, Mitt Romney, has made it clear that he will run against "Obamacare." Within hours of the Supreme Court's ruling, the former Massachusetts governor asked voters to throw Obama out of office to get rid of the law, which he promises to repeal and replace if he wins the White House in November.

There have been some early signs that appeal is working. On Friday, Romney's campaign said the former Massachusetts governor raised $4.6 million in the 24 hours following the Supreme Court's decision.

Romney has offered few specifics on how he would replace the Obama reforms, although he said he would work to retain popular provisions such as blocking insurance companies from forbidding coverage of patients with pre-existing medical conditions.

The Reuters/Ipsos poll showed little change in the strong support for that and most of the other major provisions of the bill, including requiring companies with more than 50 employees to provide insurance for their employees and allowing children to stay on their parents' insurance until age 26.

Most Americans still oppose the requirement that U.S. residents own health insurance, the so-called "individual mandate," which the Supreme Court found was constitutional under the government's right to impose taxes.

Despite the court labeling the mandate a tax - which Republicans have seized on in campaigning against Obama - the new survey found support for it unchanged. Thirty nine percent of all Americans backed the mandate, compared with 61 percent who opposed it.

Obama has credited the state plan Romney instituted as Massachusetts governor, which used a system of subsidies and mandates to expand health coverage, as a blueprint for his national plan.

The survey interviewed 991 Americans online from June 28-30. The precision of the Reuters/Ipsos online polls is measured using a credibility interval. In this case, the poll has a credibility interval of plus or minus 3.6 percentage points.

(Editing by Alistair Bell and Doina Chiacu)

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