President George W. Bush is ready to escalate his battle with Congress over children's health insurance, planning a Wednesday veto of a bipartisan bill that would have dramatically expanded the program.

It would be only the fourth veto of Bush's presidency, and one that some Republicans fear could carry steep risks for their party in next year's elections.

The White House sought as little attention as possible for the veto on Wednesday, saying the president planned to execute it behind closed doors without any fanfare or press coverage.

The State Children's Health Insurance Program is a joint state-federal effort that subsidizes health coverage for 6.6 million people, mostly children, from families that earn too much to qualify for Medicaid but not enough to afford their own private coverage.

The Democrats who control Congress, with significant support from Republicans, passed the legislation to add $35 billion over five years to allow another 4 million children into the program. It would be funded by raising the federal cigarette tax by 61 cents to $1 per pack.

The president had promised to veto it, saying the Democratic bill was too costly, took the program too far from its original intent of helping the poor, and would entice people now covered in the private sector to switch to government coverage. He wants only a $5 billion increase in funding.

Bush argued that the congressional plan would be a move toward socialized medicine by expanding the program to higher-income families.

Democrats deny that, saying their goal is to cover more of the millions of uninsured children and noting that the bill provides financial incentives for states to cover their lowest-income children first. Of the over 43 million people nationwide who lack health insurance, 9 percent, or over 6 million, are under 18 years old.

Eighteen Republicans joined Democrats in the Senate, enough to override Bush's veto. But this was not the case in the House, where despite sizable Republican support, supporters of the bill are about two dozen votes short of a successful override.

It took Bush six years to veto his first bill, when he blocked expanded federal research using embryonic stem cells last summer. In May, he vetoed a spending bill that would have required troop withdrawals from Iraq. In June, he vetoed another bill to ease restraints on federally funded stem cell research.

In the case of the health insurance program, the veto is a bit of a high-stakes gambit for Bush, pitting him against both the Democrats who have controlled both houses of Congress since January, but also many members of his own party and the public.