Hours after President Barack Obama unveiled his health care reform plan, the White House was already dodging questions about its lack of a public insurance option and whether Senators should use reconciliation to overcome a potential GOP filibuster.

The president’s plan is built on Senate-passed legislation, which did not include a public option, because Obama believes that is “the best way forward into something that can ultimately wind its way through Congress,” White House Press Secretary Robert Gibbs told reporters on Monday.

Liberal House Democrats have long pushed for a public option in health care reform, but the Senate lacks the votes for it. The public option seems to be seeing some new life in that chamber, however. Some 20 Senators signed on to a letter to Senate Majority Leader Harry Reid (D-Nev.) last week urging him to use reconciliation and to include a public option in reform.

Gibbs declined to endorse using reconciliation to pass a public option — a provision that Obama has supported in theory but not pressed for in legislation — but said Senate leaders have the ability to bring such amendments forward for votes.

Senate Democrats in favor of a public option have “asked for a vote on the floor of the Senate. And that’s certainly up to those who manage those amendments, and to Leader Reid,” Gibbs said.

The White House will also have a fight on its hands with House Democrats over the inclusion of a “Cadillac” tax on high-cost health insurance plans. Several Members have already said they would not vote for a health care reform bill that included this provision.

Gibbs said only that House Democratic leaders were briefed on the proposal Monday morning and that Speaker Nancy Pelosi (D-Calif.) will present it to the Democratic Caucus at Monday night’s meeting.

Gibbs wouldn’t say whether Obama is prepared to press for reconciliation to get a Democratic bill through the Senate on a simple majority vote, although he hinted that it wouldn’t be out of line.

“Reconciliation, as you know, is a legislative vehicle that has been used on a number of occasions over the past many years,” Gibbs said. “I do think the president believes there ought to be an up-or-down vote on health care.”