Sen. East's passing focuses attention on status of New Right. Carolinian was stalwart backer of Reagan's conservative agenda

President Reagan's crucial stake in the 1986 elections -- especially the US Senate races -- came into sharp focus this week. The passing of Sen. John East (R) of North Carolina, one of Mr. Reagan's strongest allies on Capitol Hill, temporarily shrank the GOP margin in the Senate to 52 to 47. Further, it cut some of the ground from under the President's efforts to put conservative judges into the federal courts.

Senator East was one of those freshmen Republicans who rode into office in 1980 with the President's initial White House victory.

East and his fellow freshmen Republicans were a vital force behind ``Reaganism.'' They cast pivotal votes in favor of higher defense spending, aid for ``freedom fighters'' in countries like Nicaragua, tax cuts, reductions in economic assistance programs, and a wide range of conservative social initiatives.

The 1986 elections pose a major threat to the future of Reaganism. Without a GOP majority in the Senate, the White House would find it especially difficult to fulfill pledges to New Right conservatives.

Recently the President has stepped up his efforts on New Right issues. His administration has backed tuition tax credits for private and parochial schools and launched launched legal maneuvers against abortion, among other initiatives. It has tried to place a growing number of social conservatives on federal court benches.

East, as a close ally of New Right leader Jesse Helms (R) of North Carolina, was deeply involved in much of this. His major legislative initiative during his 5 years in the Senate was a bill that would have undercut the US Supreme Court decision legalizing abortion. East's bill, which declared human life began at the moment of conception, was defeated.

Even before his death, apparently by suicide at his home in Greenville, N.C., the right wing of the Republican Party saw its hopes dashed in the race to replace East in the Senate. He had announced that he would retire in January 1987 for health reasons, and GOP conservatives hoped to put in his place David Funderburk, a strongly anticommunist professor who served for several years as United States ambassador to Romania. Dr. Funderburk, however, was easily defeated by moderate GOP Rep. James T. Broyhill in this year's party primary.

Mr. Broyhill faces former Democratic Gov. Terry Sanford in the November election, a race in which Mr. Sanford currently holds a narrow lead in the polls.

North Carolina Gov. James G. Martin, a Republican, must now choose a temporary successor to East until the new senator elected in Nov. 4 takes office in January. He appears to have three options. He could appoint Mr. Broyhill, the GOP nominee, to serve the remaining six months of East's term, possibly boosting Broyhill's prospects against Sanford by enabling him to run as an incumbent. He could appoint East's widow, Priscilla, as an interim senator.

Or he could put the seat in the hands of an experienced, caretaker politician, such as former GOP Gov. Jim Holshouser.

A decision by the governor is expected later this week.

Meanwhile, New Right conservatives who found a willing ally in East see little to cheer about in the forthcoming elections. Republicans in states like North Carolina and California appear to be inching back toward middle-of-the-road candidates. The New Right remains a pivotal force in the GOP, but there are questions now as to whether it is growing as many conservatives hoped it would after Reagan's 1984 landslide.