WASHINGTON — 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.

"The Senate today put the emphasis of CHIP back on low-income children," said Sen. Orrin Hatch, R-Utah. "We're one step closer to continuing one of the government's most effective programs that has helped millions of children receive the care they desperately need. We spend nearly $2 trillion on our nation's health care system each year. This bill funds CHIP at $60 billion over five years — a fraction of the cost. Covering these children is worth every cent."

"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."

Sen. Bob Bennett, R-Utah, voted against the legislation, saying that the program has lost its original focus — that it covers too many adults and encourages too many families to drop private coverage for the public program.

"My concerns with this bill have always focused on the program's shift from its original intent of providing low-income children with health insurance, to moving dangerously close to a government-run health-care system," he said. "I have serious concerns with the amount of money dedicated to a program that is hailed as a bill for America's poor children, when in reality an average of 13 percent of the SCHIP dollars go to adults, and in some states like Wisconsin that number is as high as 75 percent. The sponsors of the bill say that the waivers will go away, but the fact is that adults who currently have waivers will be grandfathered into the reauthorized program."

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.