The Senate passed legislation Thursday to add 3 million lower-income children to a popular health insurance program in bipartisan defiance of President Bush's threatened veto.

The 68-31 vote, one day after the House passed a more ambitious and expensive version over bitter Republican opposition, handed Democrats a solid achievement to trumpet as they leave Washington for a summer break.

It also gave Democrats, who secured a veto-proof margin, a chance to draw a stark distinction between their priorities and Bush's on an issue that resonates with voters.

"For the life of me, I can't understand why the president would want to veto this legislation," said Sen. Max Baucus, D-Mont., the Finance Committee chairman. "It's moderate it's bipartisan, it helps low-income kids. ... It's just the right thing to do for the country."

Bush has proposed spending $5 billion to extend the program. He says the Senate's $35 billion expansion would balloon the decade-old program beyond its original mission of covering working poor children and would move more people toward government-run health care.

The State Children's Health Insurance Program expires Sept. 30.

The Senate measure now must be reconciled with the House-passed $50 billion expansion, which was paid for partly by cutting government payments to Medicare health maintenance organizations.

Both bills include hefty tax increases on tobacco products to pay for the spending increase.

The health program is designed to subsidize the cost of insurance for children whose families earn too much to participate in Medicaid, but not enough to afford private health insurance.

Through federal waivers, the program has expanded in many states to include middle-income children and adults. That has led Republicans to argue that it has become a backdoor way to extend government-provided health care to an increasing number of people.

National polls show overwhelming majorities of voters support expanding the children's health program and are more likely to support candidates who back it.