AYER, Mass Nov.1 -- Demonstrators opposed to the war in Vietnam picketed outside the main gate of Fort Devens today. They included two Harvard students.

A PFC from Fort Devens who joined the picketers during the morning was arrested by two members of the Army Counterintelligence Corps.

Stephen Underwood, 13, entered the march in civilian clothes and said he was a member of the Army Security Agency. He said he enlisted in the Army eight months ago, but had decided that he wanted to get out. Displaying his Army identification card to newsmen and hecklers who gathered around him. Underwood said "I was a private first class yesterday, and I don't expect to be tomorrow."

Only 60 March

Counter demonstrators, FBI members civilian and military police, and curious onlookers almost outnumbered the roughly 60 anti-war pickets. The marches came primarily from the New England Committee for Nonviolent Action and the University of Massachusetts Students for a Democratic Society.

Underwood was the only person arrested, although scuffles between the two groups of pickets took place all day Demonstrators stood quietly while a group of teenagers grabbed signs saying "Negotiations Now" and tore them to pieces. An Ayer resident offered the pickets a gallon can of gasoline and yelled C'mon, cowards."

George E. Cave '63, one of the two Harvard students there, was told by one man that "they ought to put you inside the gate and ship you and the whole damn bunch overseas." Josef Mlot-Mroz, a Polish refugee who has attended nearly all Boston area demonstrations, shouted "Down with Communist dupes and stooges!" and set fire to two simulated Russian flags.

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In Boston, 275,000 people -- the largest crowd ever -- turned out to watch the Annual Veterans Day parade. The chief marshal, Brig, Gen. Costas L. Caragenis, called the reaction to the parade a "direct counter attack to the protests of a small national minority against our position in Vietnam.