George Bush has continually promised that the Persian Gulf war would be different from Vietnam. Already it is in one respect: The president is going out of his way to show respect for dissenters.

The question of demonstrations came up at once. There was some dispute about the readiness of our troops; there has been none about the peace groups. They mobilized instantly, and 48 hours before the deadline fielded thousands Sunday night at the Washington Cathedral who marched, holding candles, to the White House.

Monday morning at his briefing, presidential press secretary Marlin Fitzwater was all but invited to discount dissenters. He declined.

"Of course they matter," he said. "We care about everyone's attitude. We believe in full debate."

He had already disclosed that Bush had sought out one of the leaders of the dramatic display, Episcopal Bishop Edmond Brownson, for discussion and prayer on the telephone.

On Tuesday, the day of the deadline, when people were hardly breathing out of apprehension and dread, there were pickets outside the White House. Among them were about 100 Peace Corps volunteers who had been evacuated from Arab countries. They chanted "Peace be with you" in Arabic and sang the song that made Lyndon B. Johnson and Richard M. Nixon gnash their teeth, "Give Peace a Chance."

Again, Fitzwater had kind things to say about protesters. The morning after the deadline, he was questioned about U.S. soldiers in the gulf who were reported to be unhappy about the demonstrations. Fitzwater rose to the defense of the dissenters.

"Demonstrations are a part of the democratic process," he said. "We have come to accept them and their value in a democratic society."

In other words, Bush is going to profit from the mishaps of his predecessors, both of whom were driven from office by their vicious quarrels with a large segment of the citizenry over a war that didn't have to be fought.

The impact of demonstrations is still argued with enormous bitterness. History suggests that presidents, although outraged by the sight of huge manifestations of citizen disapproval, do not change their minds about ruinous policies. The anti-war movement turned out hordes but Johnson went down clutching the viper of Vietnam to his bosom. Nixon, elected on a promise to "win the peace," kept the war going for four more years. It was still in progress when he was turned out of office.

But dissenters can blight a presidency, take all the joy and juice out of it. And, as we have seen in two cases, they can end a presidency. Dissenters, particularly if they are violent and obnoxious, can create sympathy for a besieged president, but in the end they bring out the worst in a chief executive and show his unworthiness.

Johnson railed against dissenters, as he did against reporters who wrote critically about the war, and incurred the enmity of a generation. Today's passive campuses have produced little resistance, but in the '60s, college students stood in the streets, shouting, "Hey, hey, LBJ, how many kids did you kill today?"

Johnson could not travel freely in his own country. He was reduced to visiting military bases. Nixon, John Dean told us in the Watergate hearings, was unhinged at the sight of one lone demonstrator in Lafayette Park across from the White House. He announced grimly that "to allow government policy to be made in the streets would destroy the democratic process." He ostentatiously watched football reruns during a demonstration in 1969, when the White House was ringed with buses.

Bush's "kinder gentler" approach to opponents of the war could serve him well if it lasts. It could defang the dissenters up to a point, and demonstrate to the rest of the country that he is a tolerant, disinterested sort of person, not a self-pitying paranoid like the other two presidents who insisted on fighting an unpopular war.

The other haunting anti-war song, which we may be in for hearing endlessly once again, poses this question:

"When will they ever learn?"

In the case of George Bush, in the matter of fashioning a small trap for a large country, we would have to say, "Never."

But on the secondary question of Vietnam, tolerating dissent, he may have noticed how destructive it was not to. If the war is short, he can probably stick to it. If not, we can look forward only to the dismal prospect of hearing once again that it is unpatriotic to disagree with the leader of the world's greatest democracy.