It's been said so often it's become a cliche': Pity the person who succeeds Ronald Reagan; what a tough act to follow.

That's been evident for a long time, as far as the ceremonial duties of the presidency are concerned. No one does them better than Reagan. When it comes to a patriotic occasion, a memorial service or a religious observance, his words, his bearing, his expressions and gestures all speak eloquently for the American people and nation. He has set a standard that will be hard to match.

But as we approach the final quarter of Reagan's White House service, it becomes clear that he will also be a tough act to follow in several more substantial -- and worrisome -- ways.

It's increasingly obvious, for example, that Reagan is going to leave it to his successor to curb the rampant red-ink spending that has been the hallmark of his administration. Last week the White House rebuffed the latest in a five-year sequence of Senate Republican efforts to reverse the continuing tide of budget deficits.

Senate Budget Committee Chairman Pete Domenici (R-N.M.) and his colleagues offered Reagan a compromise that would provide the increased military spending Reagan demands -- if he agrees not to veto the revenues to pay for it. Nope, said Reagan, I want it all my way: more defense dollars and no taxes. So the budget impasse continues, despite the supposed Gramm-Rudman-Hollings ''cure.''

Note that the current stalemate involves the fiscal 1987 budget, which controls spending until 15 months before the end of Reagan's second term. It becomes obvious that he is going to punt this problem to his successor.

And that person's hands will be tied by the effects of Reagan's eight years of spend-now-pay-later fiscal foolishness. The bills will come due with interest -- the mounting interest on a national debt that has more than doubled during Reagan's tenure. How much more it will grow in the 30 months Reagan has left can only be guessed, but indications are the administration has once again underestimated the deficit for this year and next, so the news is likely to be worse than we know.

Another Reagan legacy, it's increasingly clear, will be the frustration of those followers who voted for him twice in the belief he would deliver the changes in abortion policy, prayer in schools and other social issues that they ardently desire. They have gotten little but lip service from this administration.

Yes, Reagan has appointed hundreds of conservative judges. But in the sixth year of his tenure, the Supreme Court has again affirmed, by a 5-4 vote, women's right to terminate pregnancies. And it has left intact the constitutional barrier against state-sponsored school prayer.

Reaganites may throw the ''blame'' on those superannuated liberal justices who are too stubborn to resign or die. But what will stick in the throats of true believers and come back to haunt his successor is the fact that Reagan repeatedly has made it plain that the social-issue agenda always takes second place in his priorities.

In 1981 the president convinced the prayer-and-abortion constituencies that his economic program had to come first. They swallowed hard, but agreed. And now it's five years later, and guess what? Economics still trumps morality.

When Senate passage of the tax-revision bill was threatened last week by the prospect of protracted debate over a suggested antiabortion amendment, Reagan persuaded the amendment's sponsors to withdraw it.

Reagan can get away with that tactic, just as he can get away with doubling the national debt, because none of his supporters thinks him capable of duplicity. He projects such sincerity that he is never accused of hypocrisy.

But at some point, those who have gone along with Reagan are likely to say, ''The rhetoric is wonderful, but when do we see results?'' If Reagan escapes that rude question, his successor is not likely to be as lucky.

The backlash will be greatest if that successor is a Republican -- be it George Bush, Paul Laxalt, Jack Kemp or Bob Dole -- who has tried to identify himself closely with Reagan. He will reap the benefits of Reagan's successes in cutting tax rates and confronting communism. But he will also have to face the fact that the unfulfilled Reagan promises to cure the deficit and rewrite the Constitution are crippling in one case and controversial in the other.

But it won't be just conservative Republicans who will have to confront that uncomfortable legacy. The deficits will make it difficult if not impossible for a liberal Democratic president to attack unemployment, improve education or reduce the nation's growing economic inequality. And the frustration of Reagan's social-issue constituency will fuel continuing controversy and civil strife on those emotional issues.

He really will be a tough act to follow.