White House lobbyist Max L. Friedersdorf said yesterday he expects the administration eventually to win congressional approval of the proposed sale of AWACS planes to Saudi Arabia.

Friedersdorf also told reporters at breakfast that he would oppose any all-out effort in the next election to defeat 21 House Democrats who have been voting consistently with the president.

Friedersdorf, a former chairman of the Federal Election Commission, said, "I would not be for abolition of the FEC." He disclosed the requirement that politicians discose campaign receipts and spending is an "excellent" feature of federal election law. But he said detailed requirements sometimes associated with FEC enforcement of the law could use cleaning up.

The administration's proposed sale to the Saudis of five AWACS airborne radar systems, designed to spot attacking planes far sooner than otherwise possible, has produced substantial opposition from members of Congress who fear it could weaken Israel.

Last week, a majority of both chambers, 224 House members and 54 senators, criticized the proposed sale in resolutions or a round-robin letter. This criticism in itself has no binding formal effect, but Congress does have a veto over the proposed transaction once it is formally sent to Capitol Hill, which the administration hasn't done so far.

Friedersdorf said he doesn't have a hard count yet, but that he believes the sale will win approval when finally sent up. He said "nothing's changed as to the idea of a package, but on the makeup of the package, it is still being decided by State and Defense."

Friedersdorf said that on last week's budget voting, when President Reagan's substitute narrowly won in a series of seven House votes, 21 Democrats led by such members as Phil Gramm and Kent R. Hance of Texas And G.V. (Sonny) Montgomery of Mississippi backed the president on all seven votes.

"These 21 are people I think are going to be with him through thick or thin. . . . I would not want to see an all-out effort to defeat those 21" in next year's election, he said, adding, however, that local Republicans might have other ideas and it would "declare these 21 districts" completely "offlimits."