President Reagan said yesterday that he is giving "top priority" to winning passage of the tax-overhaul measure approved by the Senate Finance Committee, and he appealed to Congress to reject attempts by "special interests" to amend it.

Borrowing the slogan of First Lady Nancy Reagan's campaign against drug abuse, the president said members of Congress should "just say no" to lobbyists who want to change the tax proposal.

White House officials said Reagan plans to stress the tax measure during the next few weeks in speeches devoted to the theme that administration policies are especially beneficial to young Americans, a target group for Republicans in this year's elections.

A senior official said that Reagan is doing this because he wants to be "associated with the new and the productive, the youth of America" and that this emphasis on youth dovetails with promoting the tax bill.

As approved by the Senate panel, the measure would replace the present 14 federal income tax brackets with two, 15 percent and 27 percent, while eliminating or restricting many tax breaks.

Administration officials have said they think that this will be particularly popular among young families, most of whom would be in the 15 percent bracket and have proportionately fewer tax shelters.

Reagan's speech yesterday to about 150 supporters in the Old Executive Office Building emphasized the tax measure's benefits to people in business. He said current provisions aimed at encouraging business expansion have too often been used as "escape vehicles" by corporations seeking not to pay taxes.

"Those of you who've been working long hours, in part to make up for the taxes your competitors aren't paying, will be pleased to know: The day of the free ride is over," Reagan said.

The president has expressed enthusiasm about the bill since it cleared the Finance Committee last week. He praised it during a news conference at the Economic Summit in Tokyo and subsequently called committee Chairman Bob Packwood (R-Ore.) to congratulate him on moving it to the Senate floor.

Reagan has declined to comment on specific and potentially controversial provisions of the bill, such as its ban on Individual Retirement Accounts (IRAs) for individuals covered by a company retirement plan. But he seemed yesterday to give almost blanket approval of the bill in its present form.

"The proposal that passed the Senate Finance Committee meets the criteria I set down for tax reform. Starting right now, getting it passed and signed into law is a top priority," he said.

A senior official said yesterday that the White House does not intend to become involved in specific battles on amendments as long as they do not affect the major objectives of the legislation.

The administration's emphasis is expected to be on pushing the measure through the Senate -- which plans to consider it June 2 -- in the belief that it would then be relatively easy to resolve differences between it and the House version in a conference committee.

The House plan would allow IRAs for most Americans and greater deferral of taxes in company retirement plans.

A senior official said he expects that the final version will compromise on this issue.