NOW THAT the Senate has rejected attempts by Jesse Helms and others to permit states to ban abortions and write school prayers, we can expect President Reagan and other Republicans to raise these issues on the stump. In the short run, it may be good tactics, distracting voters from what many regard as the failure, or at least lack of success, of Reaganomics. And on these issues, Mr. Reagan and the Republicans can portray themselves still as dissatisfied outsiders to an electorate that reflexively expresses dissatisfaction with the status quo.

But the short-run gains seem limited: abortion is an issue on which most voters -- particularly young voters with weak party preferences -- do not share Mr. Reagan's views, and few voters feel strongly enough about school prayer to cast their votes solely on that issue. And in the long run, issues such as abortion and school prayer may prove more harmful than helpful to those now raising them.

We say this first of all because these are, for so many voters, basically moral issues, and yet inevitably, in the give and take of political conflict, the moral purity of any position is compromised. This has already happened, as opponents of abortion agree to support a constitutional amendment that would give states their choice on the issue -- which would mean allowing abortion in many states. If you believe that abortion is murder, that is not a morally appealing position.

The other reason that emphasis on moral issues, such as abortion and school prayer, may turn out to be politically counterproductive is that such emphasis tends to promise more than government can deliver. Advocacy of school prayer and opposition to abortion are positions that, for many voters, symbolize attitudes and concerns that are larger and more difficult to articulate. The majority of voters who want school prayers permitted want this not simply because they want children to mumble a few religious words in class each day; they want symbolic endorsement of a set of values they sense that many Americans -- especially younger Americans, of the generation just becoming parents -- do not respect. Many opponents of abortion not only want to stop abortion, but would also like to discourage what they regard as immoral sexual practices.

Can government action achieve such goals? We doubt it. Government action has on occasion genuinely changed people's minds as well as their behavior -- we have in mind the civil rights laws. But generally the power of ideas and cultural attitudes are stronger than the power of government. If parents do not want to raise their children in the moral atmosphere advocates of school prayer are seeking, if 1.4 million women each year continue to want abortions -- in those cases, any laws Congress can be persuaded or bludgeoned into passing are not going to do much to change everyday life.

As these issues are debated more, we expect that voters will sense this -- just as they discovered, after the-law-'n'-order issue had been raised in a few elections, that there is not much the president or members of Congress can do to stop crime. Then those with genuine moral concerns can go about the business of making their views prevail in the marketplace of ideas, and politicians can make promises on economic and foreign issues on which government is capable of delivering.