About 100 protesters, vowing that they would never forget and shouting anti-Soviet slogans, marched near the Soviet Embassy yesterday to denounce that government's downing of Korean Air Lines Flight 007 a year ago today.

They came with placards and flowers, grasping sickles and hammers. The demonstrators set up a symbolic cemetery with paper and wire headstones bearing the names of all 269 known victims aboard the doomed plane that strayed into Soviet air space and was subsequently shot down over the Sea of Japan.

"These people do not want to forget what happened," said Charles A. Moser, a George Washington University professor of Russian language and spokesman for the march and rally in Lafayette Square. "Some people have short memories, and some memories need to be lengthened."

One woman was arrested during the rally when she and several other protesters clashed with the anti-Soviet demonstrators. U.S. Park Police said they charged Ellen B. Thomas, 37, with disorderly conduct after she entered the rally with a sign reading "Love Thy Enemy."

Ludmila Foster, a Voice of America journalist whose broadcasts are heard in the Soviet Union, tried to dissuade the intruder, saying her sign would "insult" the demonstrators.

Two park police officers quickly handcuffed Thomas and took her away. She was released yesterday after posting a $10 bond, police said.

Shortly after the noontime rally began, it became apparent that the organizing group, the Ad-hoc Coalition to Commemorate the Korean Airline Massacre had gathered to condemn not only the downing of Flight 007, but communism around the world.

For nearly 90 minutes fervent anti-communist speakers, some from nations within the Soviet sphere, spoke of mass suffering, corruption, death and deceit at the hands of communist rulers.

"What we are protesting is not a single incident," said Kurt Lohbeck, an independent producer who has filmed the Soviets' war in Afghanistan. "What we are protesting is merely not 269 people murdered on one afternoon.

"What we are protesting is the fact that it is a mere example of what [the Soviets] have been doing every day since 1917 . . . "