WASHINGTON – President Bush vetoed the state children’s health insurance bill Wednesday morning, only the fourth veto of his presidency.

Last week, Congress passed the legislation that would have expanded the State Children’s Health Insurance Program to cover an estimated four million more children at a cost of $35 million over five years. The program is designed to provide health insurance for children in families who earn too much to qualify for Medicaid but not enough to afford private insurance.

All four Maine congressional members quickly denounced the president’s decision.

Republican Sen. Susan Collins called the veto “a tremendous mistake.”

“This is a program that has been cost-effective and has had a significant impact in reducing the number of uninsured children, not only in Maine but across the nation,” Collins said in an interview. “At this point, I hope that the president will be finally willing to change his mind if there are a few – and I hope they are minor – changes in the bill. But of all the bills to veto, I think the president really made a mistake on this one.”

Sen. Olympia Snowe agreed.

“I believe this action seriously misjudges the genuine concern Americans have about access to care, particularly for children,” Snowe, also a Republican, said in a written statement.

Democratic Reps. Tom Allen and Mike Michaud also expressed their dismay at the president’s decision.

“President Bush’s veto of this bill is a blow to working families in Maine and across the country,” Michaud said in a statement. “These are Americans who work, play by the rules and simply don’t have enough income to get health care coverage for their kids.”

Despite his veto, President Bush said he is “more than willing” to work with Congress in order to maintain the program. He has said he opposes the bill because he fears the expansion would cause families to drop their private insurance and sign up for the federal program.

The president said he is willing to compromise with Congress “if they need a little more money in the bill to help us meet the objective of getting help for poor children.”

Allen said Bush’s basic understanding of the bill was incorrect.

“The bill does not, as the president claims, extend coverage to children whose families can afford private insurance from private companies,” Allen said in a statement. “This legislation would provide coverage for all children, including 11,000 additional children in Maine, who currently qualify for [the program] but have been left out of the program because the president and past Congresses did not provide the necessary funding.”

Democratic leaders have scheduled a veto override showdown for Oct. 18 to allow two weeks for pressure to build on Republicans. A union-led organization said it would spend more than $3 million trying to influence the outcome. “It’s going to be a hard vote for Republicans,” said House Speaker Nancy Pelosi, D-Calif.

Collins said the Senate has the votes to override the veto, but cautioned the House may not.

Republican leaders expressed confidence they have enough votes to make the veto stick in the House, and not a single senior Democrat disputed them. A two-thirds majority in both houses of Congress is required to override a veto.

Collins remained optimistic.

“Unless the president shows good faith, it may be possible for us to pick up additional votes in the House and override his veto,” she said.

The Associated Press contributed to this report.