At least a million Americans joined yesterday in the largest anti-war demonstration in the nation's history. From Boston to Berkeley the Moratorium supporters heard speeches, conducted marches, and held silent vigils demanding an immediate withdrawal of U.S. troops from Vietnam.

The four largest rallies-in Boston, New York, Minneapolis, and Philadelphia-drew a total of 500,000 people. The few outbreaks of violence were reported very mild. At one in front of the White House, five people were arrested.

It was a day, too, for those who support President Nixon. People opposed to the Moratorium displayed flags. drove with their car headlights on, and listened to speeches. Sen. Barry Voldwater (R-Ariz.) told one crowd in Anaheim, California, that "Moratorium participants are playing into the hands of those whose business it is to kill American fighting men."

In Vietnam 15 of those fighting men wore black armbands to protest the war while on patrol in a battle zone.

College towns were the center of most of the Moratorium activity. Though most college students did not object to the protest, in the deep South demonstrators clashed with anti-Moratorium students. Despite this, at Duke University and the University of North Carolina officials reported that only slightly more than half of the student body attended classes.

At other universities, however, Moratorium activities accounted for small percentages of student bodies. At Texas Tech 300 of 19,500 students demonstrated; at Oregon State about 1,000 of 15,000 turned out to hear talks; at Temple University about 1,000 students out of a total of 34,000 attended a vigil.

In Berkeley, California, many Morator-ium events were rained out. But a crowd of 5,000 gathered in front of the main entrance to the university to pass out pamphlets urging students not to attend classes. Class attendance was down by 60 percent according to the Berkeley's Daily Cal.

Off campus, the movement reached into the churches where special services were held. Even the World Series was affected. About 200 students stood outside Shea Stadium distributing leaflets, but inside the flags flew at full mast. Mayor John V. Lindsay had ordered the flags at half mast, but representatives of three armed services in the honor guard for the flag raising refused to go in the field unless the flag was hoisted to the top of the pole.

In New England the pattern was similar to-if more intense than-the rest of the nation. Sen. Edward M. Kennedy '54 (D-Mass.) told a World Affairs Council meeting in Boston that the United States should "announce a firm schedule for withdrawing all its troops from Vietnam as a step towards a political settlement of the war."

He called for "an irrevocable decision to remove our ground combat forces as soon as possible, but no later than one year from now, and our air and support troops promptly thereafter, but no later than the end of 1972."

Kennedy said that such a step would "force" the South Vietnamese Government "to begin making the political accommodations for the future."

Also in Boston armed Army troops were ordered to Fort Devens in the event that trouble occurred during the demonstrations. Troops were also on call in Rock Island, Ill., but were not used as the Pentagon reported that the national situation was "generally quiet."

The demand for immediate withdrawal by the national Moratorium committee was watered down in several of yesterday's speeches. Bill D. Moyers, former aide to President Johnson and publisher of Newsday, told an overflow crowd of 900 in Trinity Church in New York that the war should be ended "in whatever way the President decides."

In New Britain, Conn., flags flew from utility poles on orders of Mayor Paul J. Manafort, who urged citizens to fly flags from their homes as well to "help serve those who have doubts that we remain the United States."

Moratorium Day began with candle-lit vigils Tuesday night and meetings in several colleges, some of them in freezing weather. In Albany, New York, a group of students spent the night huddled around fires in blankets and sleeping bags while temperatures hovered in the low 30's. In Fort Lauderdale, Florida, about 100 students, many in bathing suits, attended a dawn rally.

One of the final Moratorium activities took place late last night in Providence, R.I., after a rally of 12,000 persons at the state-house, some 200 antiwar demonstrators marched through the downtown business section, singing "God Bless America."