President Bush and Congress are on a collision course over something that most Americans would agree is a good thing: government-sponsored health insurance for poor children. The argument is not just about money — although that's a big part of it — but about overarching questions surrounding how far government should go to provide such coverage.

At stake is the future of the State Children's Health Insurance Program, or SCHIP. The $5 billion-a-year program covers about 6.6 million lower-income kids whose families don't qualify for Medicaid.

Bush backs a $5 billion boost over five years, which he maintains would essentially serve the children who are covered now. But the Congressional Budget Office suggests that it would take about $14 billion more over five years in SCHIP spending to maintain the program as is. That could knock thousands of kids from the rolls.

The Senate and House want massive increases to cover more kids who are eligible for the program but haven't signed up yet.

A proposal that won bipartisan support in the Senate Finance Committee would cost an extra $35 billion over five years. It would allow 3.2 million uninsured kids to be added to the program's rolls. House Democrats talk of spending $50 billion to cover 5.1 million more uninsured kids.

There's reason to be wary of too huge a cash infusion here. An expansion of this program would include not only the low-income uninsured, but also many families who buy private insurance through an employer. It would encourage some parents to switch from private coverage to the government program. That's called "crowd-out," as in the government crowds out the private market.

A CBO report concluded that as many as half the children who get health insurance through SCHIP had been covered by private insurance. That means the government isn't protecting the health of more children, it's merely taking on the costs for children who already have health coverage. The costs are largely shifted from parents to the government — a bad deal for taxpayers. Such transfers would probably accelerate if higher-income families become eligible for the program.

We like SCHIP as an incremental approach to provide health care for the most vulnerable population: poor children. We can support an expansion, but it shouldn't be part of a leap toward government-sponsored universal health coverage.

The best way to provide coverage in an era of limited resources is to ask one question: Who needs it most?

The upcoming negotiations on SCHIP should focus on the poorest uninsured kids who are eligible for the program but haven't enrolled. The reason that many of these eligible kids aren't signed up may not be only a matter of funding. Some have parents who don't understand or don't care about the importance of health insurance. Even if it's free or at a reduced cost, they're not interested. But many others can — and should — be reached.

The Senate bill would redouble efforts to sign up families, boosting outreach programs in rural areas and other places where enrollment lags. At the same time, it would wisely curb coverage of adults and discourage unwarranted expansion to higher-income families. We'd like to see the feds and states make even greater efforts to reduce crowd-out. But barring changes, the Senate has the right approach to cover poor kids responsibly.