PRESIDENT REAGAN'S aides, according to a report in this newspaper yesterday, have now decreed that there has been enough emphasis on religion in the Republican campaign and that it's time to shift the focus to other issues. The implausible statement from campaign director Edward J. Rollins that religion "is not a campaign theme of ours" comes just before Democratic presidential candidate Walter Mondale is expected to hit Mr. Reagan for what he has been saying, and suggests administration anxiety at the hostile reaction so many people have had to the Reagan campaign's dalliance with evangelism so far. We see no reason for anyone to fall silent on the subject now just because Reagan strategists are having a case of nerves. As theologian Harvey Cox says on our Topic A page today, this is not something that, once raised, can be easily or rightly dismissed.

Republican strategists have made no secret that they are targeting the evangelical Christian vote this year. They are especially interested in detaching white southerners of fundamentalist and evangelical religious views from their traditional Democratic allegiance and bringing them into the Reagan and Republican ranks. They are working with evangelicals to register hundreds of thousands of new Reagan voters. They want their party and their candidate to be uniquely identified with the traditional religious views and moral standards which are the central focus of the lives of so many Americans.

The Reaganites are not the first to play this political game. Jimmy Carter stressed his status as a born-again Christian in 1976, and black ministers played a critical role in Jesse Jackson's campaign this year, raising money and registering voters. But, as the ultimate political fates of the Carter and Jackson candidacies suggest, there are dangers in a religious strategy -- as the Reagan campaign is evidently coming to realize. Claiming that one's own cause uniquely embodies morality or religious tradition may attract some voters, but it will repel others. Will the hot-tubbers of California or the affluent suburbanites of the industrial states rally to a standard raised aloft by the Rev. Jerry Falwell?

Claiming that one's cause is uniquely moral also invites special scrutiny and counterattack. To the extent that Mr. Reagan has used these grounds to criticize Mr. Mondale (the son of a minister) and Rep. Geraldine Ferraro (who attends Mass faithfully), he is likely to generate assaults on his own various failures to follow a strictly religious or moral way of life.

Finally, identifying your political cause with a particular set of beliefs -- as Mr. Reagan has, up until now anyway -- sends a message to those who don't share them not only that their support isn't wanted but that thee may be little room for them in the candidate's vision of America.

No wonder the Reagan campaign is having second thoughts about what it has done.