On Wednesday you could read in one front-page story that the White House was exhaling in relief that the Catholic bishops had moderated their letter on nuclear war and in another front-page story that President Reagan was still rejecting appeals by leading senators of his party to scale back the dimensions of his defense buildup.

But if well-considered compromise in the service of consensus on national security is good for the opposition, why is it not also good for the president?

Nothing is so disconcerting to people who wish Reagan well as his reluctance to adopt as his own terrain the broad middle ground that is so plainly there begging to be occupied and expanded.

It may be true that in the end he will come around and do the sensible thing. Reagan the bitter-ender is, after all, the man who has filled major posts with people who leave his core constituency muttering. He is the man who, after two fiascos, snubbed his own defense apparatus and handed off key nuclear issues to outsiders.

But he continues to display on security issues a seemingly blind rigidity. It adds great and unnecessary tension, domestically and internationally. He buys some of the worst of both worlds: by coming on inflexibly, he does not so much intimidate his adversaries as dismay his natural supporters and allies, and by following a pattern of making late concessions, he encourages his adversaries to wait him out. The policy process becomes a charade.

The defense budget fight is typical. Support for defense increases remains high, but Reagan has lost the initiative. The MX dispute dramatized to a broad public the weaknesses of his defense planning. The economic crisis opened a wide new avenue for challenges to conventional thinking.

Defense alternatives continue to flow, as you might expect, from Reagan's left: from liberals who do not share his alarming and sometime provocative view of the world scene. The real news is that serious alternatives are now emerging from the right: from conservatives who agree that the world is a dangerous place but who feel that more defense can be bought with less money than he has in mind.

Fixed as he is on the question of American credibility, Reagan worries that reasonableness may be taken as weakness and converted to American loss at the arms control negotiating table or in regional tugs of influence. But this is a way to create a perception of weakness where otherwise none might exist. Moving off a position not so much because one's adversaries reject it as because one's allies or citizens lose stomach for it: that is what Reagan has brought on himself. That is weakness.

In dealings with Europe, the president has been under pressure to accept the State Department's advice to bend on trade and defense questions. The department has its failings, but it understands that what is important about relations with Europe is relations with Europe. Achieving a given set of words or numbers with the Soviet Union counts less than sharing a set of words or numbers with the allies--to a point, anyway.

The president resists a similarly sensible approach to Congress on defense. Rather than move graciously toward the beckoning consensus, he digs in, asking his friends to trample on their better judgment--a judgment that they suspect, moreover, is likely to be vindicated in the end. Reagan has trouble recognizing a good thing.

Defense is not the only large policy area in which his ability to take command of a waiting army will be tested. A broad- based commission led by Brent Scowcroft is about to report back to him its recommendations on strategic arms and arms control. The commission has worked hard to shape and sell a compromise package that differs sharply from the very personal and ideological approach the president has taken, with considerable frustration, up to now. Will he receive the package in the accommodating spirit in which it is being offered?

In respect to Latin America, meanwhile, an even more broad-based consensus position, representing a Latin spectrum as well as an American one, has just been produced by Sol Linowitz and Galo Plaza. It is in the Scowcroft mode of broadening and redefining the policy context, rather than simply coming down harder on one side of the existing debate.

Most would-be leaders must struggle for a following. On security issues, and not only on these, Ronald Reagan has available a following struggling for a leader. Will he take the role?