President Reagan would do almost anything for the MX, the huge and homeless nuclear "Peacekeeper." When the House refused to vote funds to produce it, he accused the members of sleep-walking. He wrote to Rep. Jack Kemp (R-N.Y.) strongly suggesting that if he didn't get his missile he would cancel the disarmament talks in Geneva.

All of which makes it all the more mysterious as to why he was not willing to sign a waiver to keep Harold Brown on the special MX commission he empaneled to rescue it. Some unidentified lawyers deep in the Department of Defense invoked the "conflict of interest" charge against Brown because he is a consultant to the TRW Corp., a major contractor for the MX.

Brown was called on to give the group a little bipartisan gloss (he was President Carter's secretary of defense) and high-tech luster (he is a Ph.D. in nuclear physics.) He was supposed to bring along Democrats who are dubious about spending $35 billion on a contraption that is on its 35th shelter plan.

"Conflict of interest" is so general a charge against the Reagan administration that it has almost come to be seen as a qualification.

Examples abound of appointees happily profiteering from government service and being given a pat on the head by the authorities. The president's signature on a waiver would have kept Brown.

Brown's abrupt departure from the Commission on Strategic Forces occasioned much rumor and speculation. Most of it related to Brown's previous advocacy of the much-derided race-track or "multiple protective shelter" scheme, which actually passed Congress.

Did that mean that the commission was barreling down the track back to the "dense pack" basing mode, which was laughed out of the House, and wished to rid itself of a potential dissenter?

The Pentagon sadly admits that dense pack, which involves burying 100 missiles in a great grave in Wyoming is "counterintuitive." That is Pentagonese for something that goes against common sense.

But Defense Secretary Caspar W. Weinberger yearns for it and is convinced--as so many administration officials are about other problems--that there is nothing wrong with the merchandise, only with the sales pitch. To correct the problem, the administration has brought back from Bermuda its ace congressional lobbyist, Max Friedersdorf, who is much prized by Republicans.

But Brown says his imagined dissent was not at question. He attended three meetings of the commission, which is heavy with hawks of the like of Richard Helms, Alexander M. Haig Jr., Brent Scowcroft and Bill Clements. Nothing of substance was discussed, he said, nobody tipped his hand.

He said he thinks there was nothing sinister about the events that led to his withdrawal.

"I am willing to take it at face value," he said from his office at the Johns Hopkins School of Advanced International Studies. "My interpretation is that it was mishandled. I am annoyed, but not suspicious."

Evidently the White House, in its haste to convene a high-powered body, did not turn up Brown's TRW connection before announcing him. He made no mystery of it, and told the White House after he learned, on returning from a trip to Europe, that he had been named to the commission.

When the conflict of interest was belatedly raised by Pentagon lawyers, the president, who could have put an end to the whole thing by signing a waiver, sent the matter to Weinberger, who booted it to undersecretary for research and engineering, Richard D. DeLauer.

DeLauer was willing to give the green light to Brown, but he is a retired vice president of TRW, and Brown felt it would not "solve the perception problem." Neither would other suggestions about suspending his consultant arrangement with TRW, "which did not look good to anyone, including me." He will serve as a "special adviser" to the group.

A Pentagon official, explaining the president's sudden niceness on the conflict issue, said, "It is not wise to overrule the lawyers."

But if the panel is in a dense pack of difficulties, the missile is in more. That is according to no less an authority and MX fan than Sen. Paul Laxalt (R-Nev.), the president's best buddy in the Senate and the new general chairman of the Republican Party.

Laxalt surprised viewers of "Face the Nation" by saying that the MX is in serious trouble, and counted the ways: "people who never wanted the MX, people who wanted smaller ones . . . budgetary considerations and the nuclear freeze."

If Laxalt is right, not even the town's new hero, Redskins' fullback John Riggins, in white tie, top hat and tails, if pressed to serve, could get the MX down the field.

Having seen the president's budget, Congress' mind is more on orphans than on orphan missiles.