Lovers of the old Constitution face an exceptionally difficult time. They are about to be run over by a stampede of bellowing politicians, out to preserve (1) the flag and (2) their jobs.

The House Judiciary Committee will take up a constitutional amendment next week, with a floor vote soon to follow. The more deliberate Senate will not rush quite so madly to misjudgment. It may be midsummer before the upper chamber acts. Unless the forces of reason can be mobilized quickly, a proposed amendment may go to the states this fall.

In the wake of Monday's Supreme Court decision nullifying the futile statute on flag desecration, which Congress enacted last year, forces of unreason have claimed the ramparts. They may well command a two-thirds majority in both House and Senate. In an election year, it will take a high degree of political courage to vote against an amendment ''to protect the flag.'' How could a vulnerable member defend a vote against the proposition?

''I think he could defend it at a bar association meeting,'' said Sen. Bob Dole (R-Kan.), ''but not before real people.''

The senator's cynicism may be justified. It is perilously difficult to sail against the winds of demagoguery, but the effort should be made. In Monday's decision, Justice William Brennan said all that needs to be said. A year ago, when the high court nullified a Texas statute on flag burning, Brennan defined a bedrock principle underlying the First Amendment: ''It is that the government may not prohibit the expression of an idea simply because society finds the idea offensive or disagreeable.'' Exactly so.

The proposed constitutional amendment would erode that bedrock principle. The First Amendment now proclaims, in simple words that exalt the very soul of our nation, that Congress shall make no law abridging the freedom of speech. For the first time in 200 years, Congress would carve out an exception. The proposed amendment would add an asterisk and a footnote: Ah, but Congress may make some laws abridging the freedom of speech.

Many of those urging constitutional amendment, among them President Bush, have the highest motives. They love their country. No one doubts it. Those who have served in the armed forces look upon the flag with special emotion. It is not their reverence but their wisdom that validly can be questioned.

But I have talked with members of Congress who understand clearly that an anti-desecration amendment chips away at the First Amendment. These members would like to vote against an amendatory resolution. Politically they dare not. What was Dr. Johnson's scathing line? Patriotism, he said, is the last refuge of a scoundrel.

Perhaps ''scoundrel'' is too strong a word for those who know in their hearts that a flag amendment is unneeded but will vote for it anyway. Maybe ''weakling'' is better. The pity is to see decent men and women playing politics with the issue. In their ostensible concern for the flag as a symbol, they forget what it symbolizes.

It symbolizes freedom -- the freedom to speak, to believe, to express political positions that may be abhorrent to the vast majority of our people. When we pledge allegiance to the flag, we are not pledging allegiance only to a piece of cloth. Our allegiance is ''to the republic for which it stands.'' Our allegiance is to ''liberty.'' In that deeper allegiance, let us stand without flinching against the gathering stampede.