There is a distinctly ill omen in the way a supposedly limping, lame-duck Congress has turned on Ronald Reagan in precisely the areas where a president needs the greatest freedom; the conduct of delicate diplomacy.

Ignoring what has to have been the most high-powered personal, prime-time appeal in memory, the House has rudely rejected the MX missile and, in the process, confounded the president's defense/arms-control strategy. The State Department writes what Senate Foreign Relations Committee Chairman Charles Percy calls a "beautiful" appeal for a lid on U.S. aid to Israel as an imperative for the president's Mideast peace efforts, but Congress couldn't care less. Over strenuous administration objections, new trade-protection measures seem almost certain to sweep through Congress, carrying with them the threat of full-scale international trade warfare. Petty vendettas continue against presidential appointees for critical State Department posts.

You don't have to be on the president's side of any of these issues to be concerned. You have only to be interested in the reasonably orderly conduct of the business of national security. That a lame-duck session should be kicking the stuffing out of whatever was left of the Reagan Myth says something unsettling about what to expect in the next two years.

The Reagan Myth, of course, was that the antediluvian arithmetic of the Electoral College had somehow converted a wafer-thin popular-vote majority into a "landslide"; that the Republican gains in Congress presaged a political revolution of Rooseveltian proportions; that the conservative wave of the future would carry Republicans into control of both houses of Congress this year. The true conservative faith, so cruelly denied a proper hearing and a fair test for so long, would now guide our destiny, indefinitely.

Myths being by nature artificially generated and vulnerable to reality, this one was badly battered in November. The conventional belief was that it might be buried for good in the new Congress. Instead -- and this is the real danger signal for the White House -- the burial has begun at the hands of a Congress that was said to be part and parcel of the Reagan "landslide." November's survivors, and presumably lame ducks as well, seem to be reading the same message: Ronald Reagan, however beloved, can be pushed around with a certain impunity.

Of all our most recent presidents, Lyndon B. Johnson would be the one most likely to feel in his fingertips the peril that this mind-set in Congress poses to any president. He was too much the pragmatist, and too little the ideologue, to be bemused by myth. He understood the contagion of defeat, even on relatively minor issues -- the congressional chemistry, once the formula has been established on one issue, that somehow weakens a president on a whole range of unrelated issues.

Meeting with his aides and advisers early in his first full term, Johnson spelled out a philosophy that the Reagan crowd might well ponder. He had won an authentic landslide. But he had no illusions that this gave him some broad "mandate." He cited Woodrow Wilson's ill-fated League of Nations and Franklin D. Roosevelt's equally ill-fated Supreme Court packing scheme as examples of the way one defeat on an issue in which the president invests large amounts of political capital can be disabling.

Applying this principle to a proposal then up for presidential decision -- whether to ask for congressional approval of a controversial multilateral nuclear force for NATO -- Johnson stared down a majority of his advisers, whose passion for the idea was not far short of the ideological fevers at work on Reagan.

Now, you can say what you will about the nobility of Lyndon Johnson's statecraft (and new biographies are saying awful things). But you cannot lightly dismiss his theory of the blood-in-the-water syndrome -- the scent of success that gathers and emboldens the congressional sharks. One senses that syndrome at work now. It can hardly be less powerful in an incoming Congress that is sure to be even more disposed to impinge on the president's foreign policy prerogatives.

The question unanswered in Ronald Reagan's first two years is whether he is capable of shaking free of the old myths to the degree that will be necessary if he is to deal with this new reality.