Behind the facade of unity that the President's Commission on Strategic Forces will display today when its 50-page report is unveiled at the White House, a perception lingers that the Reagan administration has botched the job of strengthening the U.S. nuclear deterrent.

The 11 commissioners and their consultants, who together represent some of the best brains of four administrations, will play the good soldiers in an effort to generate a bipartisan consensus behind the report, which calls for deployment of 100 MX intercontinental ballistics missiles, development of a smaller missile for the future and increased research on an anti-ballistic missile defense.

But in the privacy of the commission meetings, men who served under presidents Carter and Ford spoke critically, saying the Reagan administration had squandered time and political opportunity when it once could have had the MX for the asking.

And although they won't be making any speeches on the subject, some in the Reagan administration and close to it acknowledge that the candidate who talked much of the "window of vulnerability" became the president who widely opened it.

Commission experts say the MX missile would be nearing the flight test stage if the newly installed President Reagan had been willing to overrule candidate Reagan and accept some variation of the multiple-space basing of the MX favored by Ford and Carter.

The missile might also be well on the way to development if Secretary of Defense Caspar W. Weinberger had refrained in 1981 from farming out the much-studied MX to still another panel, the Townes Commission, which took a predictable lowest-common-denominator approach that rejected the Ford-Carter basing plan.

Even then, Congress might have been willing to stick the MX into Minuteman silos, as it will now be asked to do again, if Weinberger hadn't promoted research into a scary little proposal to fly the MX around in planes, a plan liked by almost no one except the secretary of defense.

Looking back with sorrow at this process, an administration official observed that the MX, more than any other issue, revealed the down-side of Reagan's vaunted penchant for dealing with the "big picture" and leaving details to others. When Reagan announced his first strategic forces decision calling for MX deployment Oct. 2, 1981, he knew so little about it that he had to turn even the simplest questions over to Weinberger.

The official who recalled that disastrous news conference also observed that it was in some measure the product of the attempt on Reagan's life six months earlier. Reagan recuperated from his gunshot wound splendidly for a 70-year-old, but for months afterward worked a reduced schedule in which his advisers concentrated on keeping him up to snuff on budget and tax bills then barreling through Congress, while foreign policy and defense issues were left to presidential subordinates.

By the time Reagan again was a full-time president, his national security shop was rent with internal quarrels from which Reagan withdrew until they were settled by the dual ascendancy of national security adviser William P. Clark and Secretary of State George P. Shultz.

Reagan is fully engaged in national security issues these days, too much so for some of his domestic strategists. He also is far better informed about the MX than in 1981, although not so much so that his advisers are likely to turn him loose when he finally gets around to endorsing the commission report a week from Tuesday.

The new proposal, although carefully conceived, faces an uphill fight. If it meets the fate of its two predecessors, future historians may write that the bullet that struck the president mortally wounded the MX.

White House pollster Richard B. Wirthlin has gone back into the field to measure the impact of Reagan's nationally televised "Star Wars" speech of March 23 and subsequent presidential declarations on national defense. Wirthlin had wanted to poll immediately, as he usually has done after major addresses, but other advisers thought it better to wait until Reagan gave an overview of national security in a speech March 31 to the Los Angeles World Affairs Council.

Reagan was to announce his revised proposal for limiting nuclear weapons in Europe at that Los Angeles speech, which the White House had expected would be nationally televised. But the new arms control proposal dribbled out early in the week, and the Los Angeles speech was not carried by the networks.

White House supposition, reinforced by opposition of Republican senators returning from the spring recess, is that Wirthlin's survey will show increased public skepticism about the need for an all-out military buildup and prospects of arms control. Reaganism of the Week: After viewing computer terminals at Control Data Institute in Pittsburgh last Wednesday, the president said: "I know this will kind of date me a little bit, but I want to tell you that having taken this tour and seen all that's going on up here, I don't know a single thing about anything I've seen."