"The bill I am signing will set in motion reforms that generations of Americans have fought for and marched for and hungered to see," Obama said before putting his signature on the legislation. While he said it would take four years to fully implement some of the law's provisions, he highlighted measures that take effect this year.

In a ceremony in the East Room of the White House, Obama signed the massive bill after addressing an audience that included lawmakers who supported the measure. No Republicans voted for the bill in the House or Senate, and Democrats who opposed it were not invited, White House officials said. They said those Democrats would not have wanted to attend anyway.

Before Obama spoke, Vice President Biden offered effusive praise for the president in an introduction that hailed him as a historic leader for pushing his signature domestic initiative despite long odds.

"Mr. President, you're the guy that made it happen," Biden told Obama to applause from the gathering.

Before he signed the overhaul of the health-care system, a Republican attempt to torpedo the final piece of the package failed.

After meeting Monday with representatives of both parties, the Senate parliamentarian, Alan Frumin, determined that the final element of the health package could advance under fast-track budget rules, known as reconciliation, that protect it from a Republican filibuster.

The Senate is slated to begin debate on the reconciliation bill Tuesday afternoon.

Together, the two pieces of legislation would cost $940 billion over the next decade and extend health-insurance coverage to an estimated 32 million Americans who are currently uninsured. The package is aimed at stemming the soaring growth in the cost of health-care and reducing the federal deficit by more than $1.3 trillion over the next 20 years.

After the signing ceremony, Obama headed to the Interior Department for a longer speech to a larger audience including interest groups and others who could not fit into the East Room event.

White House advisers have made clear since a divided House of Representatives passed the bill late Sunday night that Obama is more gratified by the passage of the landmark health-care legislation than by actually winning the presidency.

Now a president who has been criticized for being long on ambition and short on accomplishment has achieved something that eluded predecessors as far back as Theodore Roosevelt, who called for health-care reform a century ago.

The question annoys White House officials, even as they prepare to showcase the legislation's most immediate effects and its historic significance during events such as a trip to Iowa later this week.

"I assume the president will talk about health care for a long time," White House Press Secretary Robert Gibbs told reporters Monday. "I have no doubt that we'll be on the road extensively in the fall as it relates to health-care reform and as it relates to helping those that supported health care last night and supporting Democrats, even some that didn't."

White House officials have said since Obama took office that, if the president achieved his agenda, political success would naturally follow. But Obama is going to have to help it along, as it turns out, given the splits that have opened up within his own party during a yearlong fight for health-care reform.

With some success, Republicans have called the legislation a "government takeover" of one-sixth of the economy, even though, to the left's chagrin, it does not include a government-run insurance option. Obama's East Room signing ceremony marked a renewed effort to counter the Republican argument.

It included Americans who will benefit from the legislation's most immediate impact, some of them characters who have appeared in his speeches over the past year.

Some of those benefits that kick in this year include a provision barring insurance companies from excluding children with preexisting conditions and another that allows children to remain on their parents' health-insurance policy until the children are 26 years old.

A few of the less popular provisions will be phased in over several years, including the requirement that all Americans buy health insurance. Some states are preparing legal challenges to that element of the legislation. Gibbs said he expects those suits to fail in court.

In Virginia, a Democratic state lawmaker launched a campaign Tuesday to try to stop Attorney General Ken Cuccinelli II from challenging the health-care legislation in a lawsuit alleging the law is unconstitutional. Cuccinelli, a conservative Republican, has vowed to file suit "as soon as the ink is dry" on Obama's signature. Del. David Englin called the effort "an egregious waste" of Virginian's taxpayer dollars.

In the latest political wrangling, Republicans, led by Sen. Judd Gregg (R-N.H.), had argued that the reconciliation bill being taken up by the Senate should be stripped of fast-track protection -- a move that would essentially kill it -- because provisions related to a new tax on high-cost health insurance policies would impermissibly impact the Social Security trust fund. Reconciliation bills are prohibited from making "recommendations" that impact the trust fund.

For days, Senate Democrats have said they were confident they could beat back the parliamentary challenge, the first of many expected this week as the Senate drives toward final passage by Friday. Although the new tax on high-cost insurance policies might affect the sums collected through the Social Security payroll tax, that effect is indirect, they said, noting that nothing in the measure would explicitly impact Social Security. Democrats also noted that numerous reconciliation bills have successfully included policies with a tangential effect on Social Security, including the 2001 tax cuts sought by then-President George W. Bush.

Late Monday, Frumin sent an e-mail to budget aides from both parties, confirming that the challenge "is not well taken," according to a copy of the missive obtained by The Washington Post.

Senate Budget Committee Chairman Kent Conrad (D-N.D.) was cheered by the news: "We believe the parliamentarian is clearly correct based on the precedents," he said in a statement. Republicans did not immediately respond to requests for comment.

The ruling laid to rest a dispute that had been brewing since last week, when Gregg first announced his intent to raise the challenge while the House was still in the final throes of approving the two-part health package.

The House on Sunday approved the health bill passed by the Senate on Christmas Eve -- a tough vote for many House Democrats who disliked the Senate bill -- then passed a package of revisions to remove the most objectionable provisions. Obama opted to sign the main health-care bill into law before the Senate took up the package of revisions.

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