WASHINGTON — The House ignored a White House veto threat Thursday and approved an ambitious Democratic plan aimed at helping families find and afford day care for their children.

The House first approved the plan on a largely party-line vote, 263-158, after voting more narrowly to reject a conservative alternative that President Bush had endorsed. Final passage came on a 265-145 tally.

The House also turned back amendments limiting federal aid for church-run day-care centers.

The bill, which still must go to a conference to resolve differences with the Senate, would expand tax credits for working poor families to offset day-care expenses.

It would create a system of state-issued subsidy vouchers for parents who want to use religious day-care centers, and would expand the Head Start program for poor children.

It also would establish minimum standards for day-care centers and provide money for a new program of day care based in public schools, available for all children and free for the poorest families.

Rep. Olympia J. Snowe, Rep. Joseph E. Brennan and Gov. John R. McKernan all rallied behind the bill.

In an unusual move, McKernan signed a letter sent by 14 Democratic governors to House Speaker Thomas Foley just prior to Thursday’s floor vote endorsing the Democratic leadership’s version of the bill and opposing the conservative alternative backed by many Republicans.

During the floor debate, both Snowe and Brennan voiced support for the Democratic plan.

“Frankly, if the child-care legislation were an actual child, Congress would be charged with both abuse and neglect,” Snowe said, chiding Congress for past inaction on the proposal.

“It may have taken us nearly 20 years,” Brennan said, “but we … have come a long way from 1971, when President Nixon opposed a major child initiative as `anti-family.”‘

The votes followed eight hours of sometimes emotional debate that masked the fact that there was actually bipartisan agreement on major portions of the competing versions.

Just hours before the vote, presidential spokesman Marlin Fitzwater said Bush would veto the Democratic version if enacted. The White House’s budget office issued a statement calling the Democratic version “an exercise in fiscal irresponsibility.”

“This bill does not pay as you go; it spends as they went,” said Rep. Bill Frenzel, R-Minn. “What a weird, tortured way of taking care of children — by giving them an IOU for $30 billion.”

The House defeated on a 243-182 vote a Democratic amendment that would have made the voucher system optional for states.