Chanting "Down with the KGB" and "We Want Freedom," about 250 Afghans marched from Dupont Circle to within half a block of the Soviet Embassy yesterday where they burned a replica of the Soviet flag and demanded an end to the three-year Soviet occupation of their country.

The marchers carried anti-Soviet banners ("They can kill us but they cannot conquer us" and "Moscow is the Center of World Terrorism") in protest of the Soviet military invasion of their mountainous homeland that began Dec. 24, 1979, and has brought an estimated 105,000 Soviet troops to the Asian country.

In contrast to last year when some Afghan demonstrators clashed with police during a similar march, the protest yesterday was orderly. While the marchers listened to impassioned anti-Soviet speeches in the Afghan languages of Farsi and Pushtu by speakers who stood in the back of a yellow pick-up truck at the corner of 16th and K streets, a two-man delegation walked to the Soviet Embassy on 16th Street to deliver a petition demanding "the immediate and unconditional withdrawal of Russian troops" from Afghanistan.

Sakhi Ahmadzai, one of the two, said that an embassy representative came out to meet them but refused to take the petition. They left the petition on the steps of the embassy, according to Ahmadzai, a 36-year-old construction worker from Alexandria.

The Soviet Embassy did not return a reporter's phone call yesterday.

According to Islamic custom, the marchers were segregated by sex. Children walked in front carrying placards that read "Stop Yellow Rain," a reference to the Soviets' use of chemicals in their battle with Afghan guerrillas.

Most of the marchers were members of Washington's Afghan community, which has swelled with refugees over the past three years. Estimates vary greatly on the number of Afghans here but it is believed to number somewhere between 2,000 and 5,000.

Although Afghanistan has a long history of fighting foreign invaders, its people have never before fled their country in such numbers, Afghans said yesterday.. "This is the first time in the history of our country that our people have had to leave our country; it is a very unique thing," said Mohamad Nabi Salehi, representative of the Islamic Unity of Afghanistan Mujahideen. A former law professor in Afghanistan, Salehi said he left his country in 1981.

Beliqis Mojaddidi, 20, and her cousin, Hada Mojaddidi,18, who was dressed in the traditional black Islamic wrap, the chador, said they were marching "because the Russians came to my country."