Evangelist Marion G. (Pat) Robertson upstaged Vice President George Bush and Rep. Jack Kemp in last week's curious competition to recruit precinct delegates for the Michigan Republican convention. Robertson turned out more supporters than his rivals had expected and perhaps, when the conflicting claims have been weighed, more than they were able to recruit themselves.

What this means for the future of presidential politics is a matter of debate. But it came after other "Christian candidates" had scored upsets to gain Republican nominations in a pair of Indiana House districts, and a fundamentalist Baptist minister had drawn 43 percent of the vote in the Oregon GOP primary against Senate Finance Committee Chairman Bob Packwood.

The pattern was enough to send a murmur, if not a shock wave, through this city. Suddenly everyone was proclaiming, or warning, "The Christians are coming!"

That's right; they are. And that fact has some large and less-than-obvious consequences. The immediate stakes in Michigan were minimal, hardly more than bragging rights. Those delegates who were recruited by last week's filing deadline will, if unchallenged or successful in an August primary, be voting members of the 1988 convention, which will choose Michigan's 77 national delegates. They have from now until the winter of 1988 to decide which candidate to support.

Robertson is unlikely to be the man. Like others who want to rescue America from what they define as moral or mortal dangers, his appeal is probably greater among the political activists than in the general public. Remember Sen. Alan Cranston (D-Calif.). His zeal to save America from nuclear war fired up the Democratic activists in 1983 and won him some early straw-vote victories. But as the universe of voters expanded in the 1984 primaries, his support proved to be quite limited. So it may be with Robertson, who sees the world threatened by abortion and pornography, not radioactive blasts.

But to leave it at that is to miss the larger point. In half-a-dozen states this spring, fundamentalists have demonstrated that the surge of evangelical Christians into politics, which began in the late 1970s, is still gathering momentum and has not yet reached its peak.

This should come as no surprise. As such students of American religion as James Wall of Christian Century magazine and William Miller of the University of Virginia have pointed out, we have a long history of church-based political movements. In earlier generations, similar infusions of energy and people came from the religious advocates of emancipation, prohibition and civil rights, among other causes. Previous cycles of religious activism have lasted longer than the seven or eight years this one has been around. Our church militants will probably be more evident in 1988, with Robertson in the lead.

After outshining the field of Republican presidential hopefuls at a gathering of southern GOP activists in Nashville in March and now apparently out-organizing Bush and Kemp in Michigan, the host of "The 700 Club" and head of the Christian Broadcasting Network is very likely to jump in as a candidate for the 1988 nomination.

Again, the pattern is familiar. The church-based black civil rights movement became an expanding political force in the decade after passage of the Voting Rights Act. In 1976, blacks played a vital role in the nomination and election of Jimmy Carter. Eight years later, in 1984, they produced a presidential candidate of their own in the Rev. Jesse L. Jackson.

Eight years after white Christian fundamentalists played a vital role in the nomination and election of Ronald Reagan, that constituency will be ready for a candidate of its own in Robertson.

Will he prove to be as divisive a figure in the GOP as Jackson was among Democrats in 1984? Perhaps, but I doubt it. When I interviewed Robertson for the first time after his Nashville speech, I was struck by his political sophistication. My feeling was perfectly expressed the other day by Edward J. Rollins, the manager of the 1984 Reagan campaign, who has spent a good deal of time talking with Robertson. "Pat Robertson," Rollins said, "is a politician whose profession happens to be religion."

Rollins, like other GOP pros, thinks Robertson can strongly influence the Republican nomination, even if he is unlikely to win it. Just as Jackson pressured Walter Mondale to lean leftward in filling out his ticket and framing his platform, so Robertson can pull the Republican nominee to the right.

He can affect the race in other ways as well. By exposing early the weakness of Bush and Kemp, he may encourage still more Republicans to run -- especially Sen. Paul Laxalt of Nevada. Although his personal history and habits are even more exotic by fundamentalist standards than Reagan's Hollywood background, Laxalt comes close to matching the president's following among the Christian activists. They cherish his consistent support for their special issues, as they do his longtime intimacy and partnership with Reagan.

It would be ironic if Robertson helped open the way for a onetime Carson City gambling-house owner to be the Republican nominee. But don't bet against it.