The Republican Party, trying to capitalize on the national backlash against high taxes, yesterday launched a seven-state campaign for a federal tax cut with a visit to a backyard in Brooklyn and a town meeting in a working class suburb of Philadelphia.

It was a hard-sell, media-oriented event, more like a presidential campaign than anything else.

But the party wasn't selling a presidential candidate. It was selling the Republican-backed Kemp-Roth tax bill that it hopes will help elect local and latewide GOP candidates this fall. And it rolled but some of its biggest names for the effort.

Sitting in a wooden folding chair in Marie Assini's backyard in the Dyker Heights neighborhood of Brooklyn, party chairman Bill Brock spelled out the message he hopes voters will buy.

"The average New Yorker is paying $800 more in federal income taxes than he did four years ago," he told the neighborhood gathering of about 25 persons. "I think that's insane. If you're going to pay that kind of taxes, you want to get pothholes in your streets fixed, you can to have safe streets, you want to have decent schools for your children.But you're not getting the value for your dollar."

The Kemp-Roth bill, which gets its name from its sponsors, Rep. Jack Kemp (R-N-Y.) and Sen. William Roth (R-Del.) is the GOP's answer. It would reduce everyone's taxes the next three years by one-third cutting federal tax revenues by about $124 billion. The party aruges that the tax cut will generate an economic boom that would recoup the loss in tax dollars.

For a party so often divided by internal bickering, the Republicans have recruited an impressive array ofits national leaders and would be leaders - including former presidential rivals Ronald Reagan and Gerald R. Ford - for the three day blitz across the nation in Boeing 727 nicknamed the Republican Tax Clipper.

It stars were Senate Minority Leader Howard H. Baker Jr. (R-Tenn.)House Minority Leader John Parder (Ariz.) and the party's chief candidates for statewide offices in New York and Pennsylvania.

Buoyed by the victory of the party's chief black spokesman, Sen. Edward W. Brooke, in the Massachusetts GOP primary, and the defeat of incumbent Democrat Gov. Michael S. Dukakis in his party's primary by a conservative candidate, the party attempted to link the Kemp-Roth bill with GOP-backed state tax cut measures at each stop.

At a press conference in New York, for instance Baker, a potential 1980 presidential candidate said, "It's time to get government off your back and out of your hair . . . the Republican tax cut proposal may be the last chance for the free enterprise system in the United States."

He blamed the Democratic majority in Congress for high taxes and for keeping the Kemp-Roth bill from becoming law. The House has turned back the proposal 11 times. It has yet to come up on the Senate floor.

The New York Republican gubernatorial nominee, state Sen. Perry Duryca, followed Baker to the podium pluggin his own $2.2 billion cut plan. He called the Kemp-Roth proposal "the most dramatic step our party has taken in history." He accused Democratic Gov. Hugh Carey of rasing taxes $1 billion during his four years as governor, adding, "The people of New York have had enough."

The New York lunch-time crowd hardly batted an eye when Duryea, Rep. Bruce Caputo, Republican nominee for leiutenant govenor and Brock walked down Madision Avenue to the New York public library.

"What's this? a well-dressed man asked as the crowd pressed against a store window. "It must be a politician."

"It's Duryea," someone replied. "Who's Duryea? the man asked.

Republican candidates, however, flocked to the tax cut banner. Marie Vale, a candidate for a Manhattan general assembly seat held by a liberal Democrat fell in step behind the party Luminaries, this fall is to pass out tea bags saying. "Tea for bringing a group of supporter-carrying Vale's campaign signs with her. Her chief campaign gimmic this fall is to pass our tea bags sahing. "Tea for taxes."