Just when you thought you wouldn't have to worry about presidential campaigning for a while, a new political action committee will make its debut in early May featuring Vice President Bush in the role of honorary chairman.

The declared goal will be raising funds for Republican House and Senate candidates for 1986. The committee's larger purpose will be to do good for the vice president by doing well for other Republicans. Or, in the blunt words of a Bush strategist: "It will allow the friends of the vice president to gather outside the office of the president and establish a political organization."

Gather, indeed. Less than three months into President Reagan's second term, the once-invisible vice president has become a highly visible spokesman and would-be successor to the man he once described as the architect of "voodoo economics."

That was five years ago, and torrents of Bush praise for Reagan have gushed over the dam since. The vice president has made an art form of loyalty, and his appreciative leader has more than returned the compliments.

Increasingly, Reagan's remarks are studded with laudatory references to Bush. On Jan. 25, Reagan said in a speech that "historians will recognize George Bush as a great vice president." On Feb. 11, he told The New York Times that Bush has been "the finest vice president I ever have any recollection of." And on March 25, Reagan compared the presidency and vice presidency and declared: "There's not that much difference between the two jobs."

Bush, who once seemed immobilized by his office from promoting personal ambitions, is less bashful these days. He traveled 28,000 miles in Africa and showed up for a "photo opportunity" celebrating Senate approval of African relief. Last week Bush called attention to his increased involvement in domestic policy by chairing Cabinet meetings and preaching the virtues of Reagan's budget to businessmen and bankers.

While proclaiming unyielding loyalty to Reagan and defusing some ritual opposition of his party's right wing, Bush has assembled an independent strategy team whose members include veteran Republican pollster Robert Teeter, shrewd southern political consultant Lee Atwater and former U.S. senator Nicholas Brady of New Jersey. Bush has forged close ties with Californians whose lives have been preoccupied with Reagan, notably Attorney General Edwin Meese III and departing White House deputy chief of staff Michael K. Deaver.

Bush's best move may have been choosing Craig L. Fuller as his new chief of staff. Fuller, a former Deaver business associate, became a White House behind-the-scenes power as Cabinet secretary during Reagan's first term. He has quietly reorganized a staff that even some of Bush's friends considered an obstacle to effective pursuit of the presidency.

By the end of 1985, the well-heeled Bush backers who will form his new committee expect to have raised $1 million. They will spend this money promoting Bush's candidacy and contributing to candidates who are expected to be suitably grateful in 1988.

All this amounts to an unexpectedly rapid start by Bush, who may be spurred by knowledge that likely rival Rep. Jack Kemp (R-N.Y.) also has expanded his staff and political itinerary. Bush is trying to get out of the gate so quickly that other Republicans and the news media will assume his nomination into evidence. This assumption would be boosted by a Reagan endorsement, which Kemp considers likely.

But is George Bush inevitable? Not if recent history is a guide. With the exception of Reagan in 1984, no president or presumed front-runner in either party since Dwight D. Eisenhower has escaped a nomination challenge.

Kemp, trying to shed a reputation for reluctance, is not being coy. He has visited New Hampshire, California, Florida, Texas and Illinois at least twice each in the past eight weeks, with tax reform the centerpiece of his message. "I'm very interested in the presidency," he said last week. "I'm looking at it seriously. I don't think Bush's nomination is inevitable by any stretch of the imagination."

Bush and Kemp offer cultural contrasts and a test of whether high-visibility loyalty to Reagan and his works can overcome Kemp's conviction that "the Republican Party has to broaden its base and have some ideas to offer after Reagan." What the efforts of both men demonstrate is that the struggle to succeed Reagan has begun.