It was a kind of a "stealth" peace demonstration. There was no way of knowing how large it was until it actually arrived.

In the old peace demonstrations of the Vietnam era, it was possible to guess at the turnout by checking the people who left their buses to stream through downtown streets to converge at the White House and the Ellipse beyond.

But last Saturday, there was a new wrinkle. The metropolitan police decreed that all incoming buses must decant their passengers at RFK Stadium, several miles away from the target area. From there, they had to take the Metro to the Capitol. From there, they were to march.

The Metro, swamped by the addition of thousands, had to be shut down several times, but eventually the marchers assembled in the Capitol Plaza in freezing temperatures, marched down the Hill past the White House to salute, in their fashion, the absent occupant, George Bush.

It was then that their numbers became apparent. They filled Pennsylvania Avenue from curb to curb. Some stood on the sidewalk to cheer them on. The speaking program on the Ellipse was two hours old, and the marchers were still arriving on the windswept field. The column was a mile long.

The marchers were elated, of course, by their numbers, and by their range. A white-haired woman puffed along the line at 15th Street, pointing to the roof of the Treasury Building, where she said, the last time she walked, at the end of the Vietnam War, police had stood with guns. There were dewy high school students, too, and labor folk and veterans and a woman holding a sign that said, "Bisexuals against the war."

The speakers hailed the host as numbering 250,000. The police said it was only 75,000. However many, there wasn't a flag-burner among them. They were carrying flags instead. It isn't clear what our government learned from Vietnam, but demonstrators say its lessons for them are clear. More flags and, as Rep. Charles B. Rangel (D-N.Y.), the only member of Congress to address the host, said, "Support the warriors, not the war." It is possible, they think, to beat the rap laid on them by the pro-war groups that to clamor for stopping the war is somehow undermining the troops.

The mood was good-tempered. The war is young, and the thought that they could turn out such a horde on such short notice brought the first happy hours they had since they saw the rockets' red glare over Baghdad. The organizers, a New York group called The National Campaign for Peace in the Middle East, is composed of volunteers, and they touched some old buttons left over from Vietnam, a network that was activated again during the contra years. Much of the action was local and spontaneous. Boston sent 47 buses; there were buses from Texas, Colorado and Maine. The marchers met pockets of presidential supporters along the way. They simply engulfed them.

The signs were all homemade and often wordy. One had a complicated message linking the gulf, the S&Ls and Neil Bush. Another said, "Sorry, Iraq, we just had all these weapons left over from the Cold War." Four scruffy young men stood on the corner of 15th and G using sticks of woods to drum on three mailboxes and a waste bin and give the marching beat. An "Impeach King George" sign ran into an "Impeach Bush" sign outside the White House.

Rangel, waiting to go on stage in the bitter wind of the Ellipse, said he was not lonely, although the only national politician to speak.

"Not at all," he said, "My district supports what I am doing. My cardinal {John J. O'Connor} is against the war. So is Pastor {James} Forbes of the Riverside Church. My Baptist ministers just had a convention and came out against it. Rabbis in my district are against it."

The euphoria was pervasive. But what difference did it all make? Leslie Cagan, the chief coordinator, an anti-Vietnam organizer, said, "It does have an impact on policy-makers. The president is always the last to feel it. The congressmen and senators, they get it first and pass it up."

Yesterday morning, the president turned the other cheek. In a speech to the National Religious Broadcasters, he said of the Saturday rumpus that he has "no bitterness in my heart about that at all, no anger."

The vice president, of course, has a slightly different line. Last week, He berated the press for spending too much time on anti-war demonstrations.

He could have had no complaint with the networks Saturday night. CBS gave equal time to the 300, at most, pro-war demonstrators and the 75,000, at least, peace demonstrators. NBC limited its coverage to remarking that the turnout of 75,000 had been accurately predicted by the police department.