Chanting "Stop Soviet Murderers" and carrying signs saying "This Gutless Crime Cannot Go Unpunished," about 200 people marched yesterday from Lafayette Square to within a block of the Soviet Embassy in a hastily organized protest against the shooting down of a South Korean passenger jet.

A phalanx of police, invoking a District of Columbia law that prohibits demonstrations within 500 feet of an embassy, halted the march at the corner of 16th and L streets NW. The Soviet Embassy, which was surrounded by police most of the day, is located on 16th Street half a block from where the marchers were ordered to stop.

Heeding the bullhorn commands of a National Conservative Political Action Committee organizer, the marchers--most of them young, well-groomed employes of conservative organizations who had been recruited from area office buildings--cast down their placards, offered a prayer for the 269 people killed aboard the Korean Air Lines 747 jet, sang "God Bless America" and dispersed peacefully.

Later in the afternoon, as police kept pedestrians from walking on the sidewalk in front of the embassy, two people were arrested across the street when a crowd gathered and began shouting anti-Soviet slogans.

Police said that Nina O'Keefe May, 31, of 2310 N. Washington Blvd. in Arlington, and Kurt Lohbeck, 41, of 2732 Ordway St. NW in Washington, were charged with demonstrating within 500 feet of an embassy. They paid $50 fines and were released, police said.

After the two were arrested, police forced the crowd to move more than a block away from the embassy to the intersection of 16th and K streets, where about two dozen people continued to demonstrate into the night.

At about 10 p.m. their number swelled to more than 75 as a group of Republican college students joined the demonstration, which for a time spilled from street corners into the intersection. Chanting and shouting protesters encouraged passing motorists to honk their horns, and hundreds did, creating a cacophony that could be heard for dozens of blocks.

As police reinforcements arrived, the protesters set off on a raucous procession down 16th Street toward the White House three blocks away. Officers on motor bikes tried several times to prevent the marchers from leaving the intersection, but the crowd broke up into smaller groups along side streets, then reassembled on the sidewalk across Pennsylvania Avenue from the White House where the dmonstration continued until about 11 p.m.

A third demonstrator was arrested there and charged with disorderly conduct following a dispute with another group protesting nuclear weapons, U.S. Park police said. They said that an antinuclear placard was destroyed in the incident.

The afternoon march, which began at 2:30 p.m., followed a brief rally in Lafayette Square where demonstrators condemned the Soviet Union for shooting down the airliner and killing Rep. Larry McDonald (D-Ga.), a passenger on the plane.

"It's murder, plain murder. No other way to put it," said Rep. George Hansen (R-Idaho), who, like McDonald, has spent much of his career attacking the Soviet Union.

It was ironic, Hansen said, that a lifelong anticommunist should "end his career in martyrdom in the bloody hands of the Soviet Union."

While Hansen, NCPAC director Terry Dolan and others made speeches to reporters, a crowd of young people waved signs saying, "I Know 269 People Who Won't Support Nuclear Freeze," "Trust Russia, Never" and "God Bless America."

Dolan called the Soviet Union an "evil empire" and asked the United States to embargo all trade with the Soviets, expel Soviet diplomats and halt arms-reduction negotiations.

The rally and march were the idea of Brad Zerbe, political director of NCPAC. Zerbe said yesterday that as soon as he heard Secretary of State George P. Shultz say that a Soviet jet had shot down the airliner, he telephoned "about two dozen conservative groups."