WASHINGTON, April 18--Fifteen thousand demonstrators picketed White House Saturday demanding the withdrawal of U.S. troops from south Vietnam.

Most of the marchers were college students from more than 75 campuses from to California. With them on the six-block-long picket line were civil rights workers, high school students from Mississippi, mothers wheeling baby carriages, and a group of 70 scientists from the Rockefeller Institute.

At an afternoon rally in the outdoor Sylvan Theatre near the Washington Monument, Senator Ernest Gruening '07 (D-Alaska) told the demonstrators, We are standing on the brink of a world war of cataclysmic proportions."

Gruening said the U.S. is strengthening the impact of Chinese propaganda waging "a bloody war--costly in lives and dollars--pitting white men against and fought to a standstill by a small Asiatic country."

The United States should "recognize the clear facts of life" and negotiate an immediate cease fire with the National Front," Gruening said. After rally the demonstrators poured down towards the Capitol to present to Congress. Finding the locked, however, students leading the the petition to one of gates at the entrance.

Moments later, police formed a chain across the marble steps of the building, some of the students began calling or a sit-in. A police official then agreed accept a copy of their petition and give to a "responsible member of the government."

Shortly afterwards, most of the students dispersed to board buses out of Washington. Two students--later joined four others--stayed behind to sit-in the steps of the Capitol. They left after 11 p.m. when police threated to arrest one of them--Phillip A. a 17-year-old Freshman at Reserve College--for violation of .

White House Sit-in

Passen stationed himself in front of White House this afternoon, with other student peace from around the country, who began sidewalk sit-in at noon. The students they would stay the night and try sit-in inside the White House Monday .

Saturday's demonstration began at when about 100 students arrived the White House to picket. By 11 the ranks had swelled to well over . The picket line two blocks St.--the length of the Treasury department building--around Pennsyl- House, then up 17th St. for two blocks vania Avenue in front of the White beside the Executive Office Building.

At 1 p.m. the pickets began to march to the Washington Monument, where they sat on the grassy sun-drenched hillside nearby. They listened intently to a series of speakers on the pink podium which is nestled among the cherry trees that bloomed here last week.

Addressing the crowd, journalist L.F. Stone said of the march, "Nothing could be better calculated to rid this country's reputation of the smell of burining flesh and napalm."

"We can destroy the whole country of Vietnam," said Stone, "but we cannot win unless we are prepared to let this poor people for once decide their own destiny." Urging the United States to negotiate with the Vietcong, he said that the National Liberation Front "represents a desire for the kind of unification which will not bring the South under the domination of the North."

The only tense moment of Saturday's demonstrations came late in the morning when police suddenly refused to allow students with picket signs to cross East Executive Ave. which passes beside the White House. The demonstrators protested the order and started across the street, yelling for pickets to charge the police. As police began to push the students back to the curb, the order was rescinded