Low-income students in Washington, D.C., could get as much as $ 11,000 apiece in private-school tuition under a pending congressional proposal, dwarfing other tax-supported vouchers available to students elsewhere.

A successful District of Columbia voucher program, supported by Republicans, could be a politically potent showcase of free-market school reforms in the Democratic-controlled city, which has the nation's highest per-pupil education costs and some of its worst results. Most Democrats oppose vouchers, saying they drain money from strapped public schools.

D.C. Mayor Anthony Williams, a Democrat, last week spoke out for the first time in support of vouchers, a dramatic change in course and an indication that the city is willing to try the experiment for some of its 67,000 students.

"Now that the mayor's come out for it, I think he's given us a lot of firepower," says Sen. Judd Gregg, R-N.H., who has proposed legislation pegging a D.C. voucher to the city's per-pupil expenditure, about $ 11,000 this year. The proposal was part of an omnibus education bill issued earlier this year.

The Bush administration and House Republicans have yet to issue their voucher proposals, but the 2004 budget resolution approved last month includes $ 75 million for voucher programs and other "school choice" plans.

Gregg's proposal, available to students whose families earn less than $ 52,000 for a family of four, would be limited by private-school tuition, so that if a student attended a Catholic school that costs $ 4,000 a year, he or she would get only $ 4,000; a student attending a prep school costing $ 20,000 would still get only $ 11,000.

The nation's oldest voucher program, in Milwaukee, offers up to $ 5,500 to about 11,600 low-income students. A similar program in Cleveland gives up to $ 2,250 to about 5,000 students.

In Florida, about 500 students attend private school with "Opportunity Scholarships" that give, on average, $ 3,300 in tuition. Like Gregg's proposal, the Florida vouchers are based on school districts' per-pupil expenditures.

Legislative analysts say the D.C. program next year could sustain up to 2,000 students receiving vouchers of about $ 3,000 to $ 4,000, roughly the tuition at many religious schools. It would be built around a lottery, meaning that if many students used the full voucher, fewer students could take part.

The D.C. proposal would still be out of reach for most of the city's 67,000 students, says Marc Egan of the National School Boards Association. Local private schools have only about 1,200 slots available, he says.

President Clinton vetoed a similar bill in 1998.