Sen. Edward Kennedy plans to use "every tool available to him" to defeat the use of school vouchers in Washington, D.C., his spokesman said Thursday.

But voucher supporters are trying to change his mind, and will run a politically charged television ad in Massachusetts next week questioning Kennedy's commitment to civil rights.

Kennedy spokesman Jim Manley called the ad outrageous, and said he wouldn't "dignify it with a comment." But he said it won't stop Kennedy from trying to block legislation in the Senate that would give private school vouchers to D.C. students.

Asked if Kennedy, D-Mass., would filibuster the bill, he said the senator has not ruled anything out. Manley said Kennedy will offer an amendment to drop the voucher program from the bill and put the funding into improving Washington's public schools.

"He's committed to trying to stop this program," Manley said.

The legislation would provide $13 million so that thousands of low-income students could go to private schools and receive up to $7,500 to defray the costs. A similar bill passed in the House by one vote, but opponents believe they can stall the bill in the Senate.

The lobbying on both sides is intensifying, prompting the D.C. Parents for School Choice to target Kennedy with an ad that exploits his family's legacy as civil rights activists.

"We're frustrated to hear he is so adamantly opposed to this," said Virginia Walden-Ford, executive director of the group. "The Kennedys were always very supportive of fairness and of people getting what they deserve."

The ad shows scenes from the civil rights movement in the South, and Walden-Ford talks in the voice-over about growing up with segregation and knowing that the late Sen. Robert Kennedy fought for their equal rights.

"Senator Kennedy, your brothers fought for us," she says in the ad. "Why do you fight against us?"

But voucher opponents hail Kennedy's commitment on the issue.

"He's absolutely our hero," said Iris Toyer, co-chair of Parents United for the D.C. Public Schools. "He is a person of good conscience who will stand by his previous positions, and not do like some others and say this is different because it is the District of Columbia."

Kennedy has repeatedly blasted the voucher plan, saying it will take money from public schools and give it to private schools that don't have to meet as many testing and accountability requirements.

"Students in the District of Columbia deserve a good education, but voucher plans are not the answer," Kennedy said. "Public funds should be used for public schools, not to pay for a small number of students to attend private schools."

The D.C. appropriations bill, which includes the voucher plan, could come up in the Senate next week. Increased opposition, however, could force backers to fold it into an omnibus spending bill later this month.