WASHINGTON — House Democratic leaders said today they were working to gather votes to override a veto on a popular children’s health program, but pledged to find a way to cover millions without insurance should their effort fail.

In talk show interviews, Speaker Pelosi and Majority Leader Steny Hoyer did not dispute claims by Republican leaders that the GOP will have enough votes to sustain President Bush’s veto when the House holds its override vote on Thursday.

Ms. Pelosi and Mr. Hoyer promised to pass another bipartisan bill if needed.

“Isn’t that sad for America’s children?” Ms. Pelosi said when asked about the GOP’s assurances the override vote will fail. “It doesn’t mean we aren’t working hard throughout the country: governors, mayors, people who deal with children on a regular basis.

“We’ll try very hard to override it. But one thing’s for sure: We won’t rest until those 10 million children have health care,” she said in an interview broadcast today.

Mr. Hoyer declined to predict Thursday’s vote.

“This is a defining moment for the Republican Party, in my opinion,” Mr. Hoyer said, before adding later: The program is “not going to die. We’re going to go back and we’re going to pass another bill.”

House Democrats scheduled the vote after Mr. Bush earlier this month vetoed legislation that would increase spending for the State Children’s Health Insurance Program by $35 billion over five years. Mr. Bush has called for a $5 billion increase.

An override requires a two-thirds majority in the House and Senate. The Senate approved the increase by a veto-proof margin, but the earlier House vote fell about two dozen votes short.