President Barack Obama speaks about health care Friday in the Diplomatic Room of the White House in Washington.

Washington ? President Barack Obama, worried about growing resistance to his health care plan, exhorted Congress not to “lose heart” Friday and urged deeper cost cuts to calm concern over the huge expense of covering millions of uninsured Americans.

“What we want to do is force the Congress to make sure that they are acting” on recommendations to hold down Medicare and Medicaid spending, the president said, rather than allowing reports to sit unused on a shelf.

Aiming to rally lawmakers, he spoke from the White House near the end of a week of tumult for the legislation atop his domestic agenda.

“Now, I realize that the last few miles of any race are the hardest to run, but I have to say now is not the time to slow down, and now is certainly not the time to lose heart,” he declared.

A few hours earlier, two House committees approved their portions of the sweeping health care bill over Republican objections.

That left one more panel to act, but conservative Democrats were rebelling, demanding additional measures to hold down skyrocketing costs.

Given the complexities, as well as fresh calls for delay in the Senate, House Speaker Nancy Pelosi, D-Calif., opened the door to pushing off a vote past the early August timeline she and Obama laid out weeks ago.

Whatever the difficulties, she predicted legislation would pass that will transform the nation’s health care system, extending coverage to millions who lack it while slowing the growth in costs generally. “It is really historic. It’s transformation. It’s momentous,” she told reporters.

If anything, Obama tried to project even more confidence.

Ticking off a list of accomplishments to date, he said, “We are going to get this done. We will reform health care. it will happen this year. I’m absolutely convinced of that.”

Without the overhaul, he said, “no one’s health insurance is going to be secure, because you’re going to continue to see premiums going up at astronomical rates.”

Obama’s call for additional steps to hold down costs came one day after the head of the Congressional Budget Office told Congress the legislation taking shape so far would fail to accomplish that.

Those remarks by Douglas Elmendorf produced fresh criticism from Republicans, and gave pause to Democrats, as well.

In letters to Pelosi as well as key committee chairmen, administration budget director Peter Orszag called for additional steps to ensure the bill “rewards quality, restrains unnecessary costs and provides better care to more Americans.”

Legislation is already pending in the Senate to reduce the control individual lawmakers and Congress as a whole have over setting the rates doctors and other providers are paid under Medicare. In his letter, Orszag forwarded an alternative proposal that he said would accomplish the same goal.

“We’re very proud of the savings (already in the legislation)” Pelosi told reporters, although she added, “Of course, we want more.”

Under current law, a Medicare Payment Advisory Commission makes recommendations to lawmakers annually on the rates Medicare pays doctors and other health care providers. Lawmakers are not obliged to follow them, or even vote on them.

Obama recommended changing that, requiring lawmakers to vote on the recommendations and proposing they take effect unless rejected by the House and Senate.

In a statement released after Obama spoke, Senate Majority Leader Harry Reid said lawmakers “now stand on the doorstep” of enacting legislation.

For her part, Pelosi signaled that she, too, was open to additional cost-cutting provisions and suggested they may be incorporated into the bill next week by the House Energy and Commerce Committee.