After the facts of the Gulf of Tonkin incident began to come out in 1968, Sen. J. William Fulbright (D-Ark.), the chairman of the Foreign Relations Committee who, like 88 of his colleagues, had been taken in by the administration account of it, said: "The least I can do is to alert future Senates that these matters are not to be dealt with in this casual manner."

As originally presented on Aug. 4, 1964, two American destroyers, the C. Turner Joy and the Maddox, were fired on by North Vietnamese PT boats. This report was transmitted to President Lyndon B. Johnson, who promptly did two things: He ordered the bombing of North Vietnam, and he rushed to Congress for an expression of support that turned out to be a prescription for full-throated war.

In the Senate, with Fulbright in the lead, the so-called Gulf of Tonkin resolution passed 88 to 2, with only Democrats Wayne L. Morse of Oregon and Ernest H. Gruening of Alaska dissenting. It whistled through the House unanimously.

George Ball, the official White House dove, has said that Johnson himself "wasn't completely convinced . . . but they had been waiting for a provocation for a hell of a long time . . . and this served the purpose."

It turned out, in the case of the Maddox, that the North Vietnamese "torpedoes" actually were the U.S. destroyer's own electronic signals, which were bouncing off its rudder because of the ship's zig-zag course. The Maddox's commanding officer tried to tell Washington, but nobody wanted to hear.

The attack never happened.

This week, the Senate, just three days before a scheduled vote on aid to Nicaraguan counterrevolutionaries, or contras, was presented with an incident of similar murkiness, the so-called grand-scale Nicaraguan "invasion" of Honduras. Reagan administration officials gleefully rushed up to Capitol Hill to brief senators on this fortuitously timed vindication of administration claims of Daniel Ortega's relentless aggressiveness.

Skeptics were caught between warring impulses: their bitter acquaintance with Ortega's ineptitude and storied bad timing, and a suspicion that a routine border raid -- there are 300 on record -- was being pumped up into a Latin American D-Day to stampede them.

Ortega was damned and cursed in hyperbole worthy of President Reagan. House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.), who rallied House Democrats to reject contra aid a week ago, called him "a bumbling, incompetent Marxist-Leninist communist." Nobody mentioned that Ortega heretofore has been extremely discreet about border provocations.

Democrats felt called upon to express sympathy and support for Honduras.

Did an invasion occur? So far, all we have is Washington's word for it. The Honduran government at first denied it.

But upon Reagan's proferred $20 million emergency aid to repel the invaders, Honduras' president decided that that there had been an invasion -- although he placed it in a different province from the one cited by Washington.

We may, in due course, get the straight of it. But, as in the case of the Tonkin Gulf, it may come too late.

Are we in for it again: for "surgical strikes" and bombing pauses, search-and-destroy, enclaves, pacification, napalm, Agent Orange, Rolling Thunder, hearts and minds -- not to mention the infamous "Operation Phoenix"? Are we in for all the miseries that attend a proxy war: teach-ins, sit-ins, white papers, marches, disruptions?

Absolutely not, says Sen. Warren B. Rudman (R-N.H.). "There will be no U.S. ground troops," he said. "Congress and the people would not stand for it. . . . Reagan is much smarter than Lyndon Johnson."

Just how 6,000 contras could overcome 60,000 Sandinistas and capture and hold land is not clear. Heavy airpower seems indicated. But bombing Nicaragua back to the Stone Age, which to the regret of the right wing was not quite done in Vietnam, is a non-starter. The country looks as if that had already happened.

Nicaragua, except for the victims, could be different from Vietnam, politically not so troublesome. With the draft gone, middle-class white parents would not bedevil politicians, and the campuses would not flame. Today's youth, conditioned by the "We're No. 1" Reagan mentality, don't burn with indignation over the fate of small, uppity countries that engage the attention of U.S. presidents who believe peasants are "better dead than red."

In deciding whether to go along, Congress should at least remember the Gulf of Tonkin -- and be wary of tales of outrageous provocations.