Rep. Jack Kemp (R-N.Y.), one of Ronald Reagan's economic advisers, yesterday urged Reagan's supporters to delay demands for conservative social legislation until the President-elect's economic plan has been enacted.

"Frankly, I don't think capital punishment is the No. 1 issue for the Republican Party," Kemp told reporters. He referred to plans by Sen. Strom Thurmond (R-S.C.) to press for legislation instituting the death penalty for some federal crimes next year, when Thurmond is expected to become chairman of the Senate Judiciary Committee.

This is one of a range of social issues high on the wish lists of many conservatives and Moral Majority members, who see the Reagan victory and the election of a Republican-controlled Senate as an historic chance to rewrite social and economic legislation.

"Attacking the New Deal is a mistake for us," Kemp said. "There is little incentive for warfare against the groups and constituents that ultimately could find themselves voting Republican" if Reagan can deliver on his promise of prosperity, Kemp added.

To make good on that promise, Reagan must start very fast next year by proposing a comprehensive economic plan and pressing Congress to approve it in the first few months of the new administration, Kemp says. He and Rep. David Stockman (R-Mich.), have urged Reagan to "declare a national economic emergency" and call on Congress to clear the decks for exclusive action on the Reagan economic plan.

It isn't clear how far Reagan will go in that direction. Reagan aide Martin Anderson said recently that while Reagan intends to make a fast start, he hadn't decided whether to ask for a delay on conservative social legislation while his economic plan is before Congress.

Kemp and Stockman continue to push that theme, however. For instance, they have advised Reagan to seek an informal agreement with Sen. Orrin Hatch (R-Utah), the next chairman of the Senate Labor and Human Resources Committee, and Sen. Jake Garn (R-Utah), the next chairman of the Senate Banking, Housing and Urban Affairs Committee, to put off consideration of controversial labor legislation like a reduced minimum wage for younger workers.

"There is no point in antagonizing organized labor during this critical period," Stockman and Kemp say in a memo to the Reagan staff.

Likewise, efforts to pass the platform of the Moral Majority, including its demands for a constitutional amendment forbidding federally funded abortions, could trigger political controversies in Congress that might block approval of economic legislation, the two say.