Washington ? Cheered by President Barack Obama, House Democrats rolled out landmark legislation Thursday to extend health care to tens of millions who lack coverage, impose sweeping new restrictions on the insurance industry and create a government-run option to compete with private insurers.

But even as party leaders pointed toward a vote next week, fresh questions went to the heart of their drive to remake the nation’s health care system.

Congressional budget experts predicted the controversial government insurance option would probably cost consumers somewhat more than private coverage. Rank-and-file conservative Democrats also sought additional information about the bill’s overall impact on federal health care spending.

There was no official estimate on the total cost of the legislation, which ran to 1,990 pages. The Congressional Budget Office said the cost of additional coverage alone was slightly more than $1 trillion over a decade. But that omitted other items, including billions for disease prevention programs.

Yet another $230 billion or more in higher fees for doctors treating Medicare patients, included in an earlier version of the bill, was stripped out and will be voted on separately.

The House plan would cover an additional 36 million people by 2019, leaving only 4 percent of the nation without coverage, compared with the estimated 17 percent of Americans who currently do not have health insurance, according to a preliminary analysis by the nonpartisan Congressional Budget Office.

Speaker Nancy Pelosi, D-Calif., at a ceremony attended by Democratic lawmakers, said the legislation would reduce federal deficits over the next decade by $104 billion, and congressional budget experts said it would probably reduce them even further over the following 10 years.

While saying they expected a vote next week, Democratic leaders were careful not to claim they had yet rounded up enough votes to pass the legislation.

Across the Capitol, the Democratic-controlled Senate is expected to begin debate within two weeks on a bill crafted by Majority Leader Harry Reid, D-Nev. It, too, envisions a government-run insurance option, although states could opt out, unlike in the bill the House will vote on. That portion of the Senate version appears likely to be weakened even further, as moderates press for a standby system that would not go into effect until it was clear individual states were experiencing a lack of competition among private companies.

Republican reaction was as swift as it was negative. “It will raise the cost of Americans’ health insurance premiums; it will kill jobs with tax hikes and new mandates; and it will cut seniors’ Medicare benefits,” said the party’s leader in the House, Rep. John Boehner of Ohio. He carried a copy of the 1,990-page measure into a news conference to underscore his claim it represented a government takeover of the health care system.

Republicans have already signaled their determination to make the health care debate a key issue in next year’s congressional elections, when all 435 House seats will be on the ballot.