About 200 demonstrators, chanting slogans and waving placards, gathered at Dupont Circle yesterday to protest the Israeli invasion of Lebanon and Prime Minister Menachem Begin's lunchtime visit with President Reagan, D.C. police said.

The demonstrators assembled in front of the circle's fountain before marching down Connecticut Avenue enroute to a rally on the Ellipse behind the White House sponsored by Americans for Peace and Unity in Lebanon.

"This is a peaceful protest to show our president the killer he's entertaining in the White House is not acceptable to us," said Richard Shadyac, a Washington lawyer and the Chairman of APUL.

Marchers bearing posters that read "Begin is a murderer" and "Stop U.S. aid to Israel" lined up peacefully behind a massive Lebanese flag that covered one half of the avenue and required eight flagbearers to transport. There was a brief scuffle between pro-Lebanese demonstrators and a group carrying a Revolutionary Workers Party banner.

The orderly column of protesters made their way slowly toward the White House, chanting "Lebanon is Arab land." At the Ellipse they were joined by 200 more demonstrators, according to Park Police estimates, including the former Ambassador to Qatar during the Carter administration, Andrew I. Killgore.

"American policy in the Middle East is one of collusion with Israel," Killgore told the cheering crowd that braved the sweltering noonday heat to register their dissatisfaction with the Israeli push toward Beirut. "We must inform the American people about what is happening in Lebanon."

Many demonstrators spoke of personal and emotional ties to Lebanon. "I grew up in Lebanon," said Lori Basson-Hayes, a former student there who plans to return to the war-torn nation. "Most of the Palestinian Arabs being killed are not PLO terrorists. They are mostly displaced people. We must stop the killing."

Dr. Safa Rifka, a surgeon at Georgetown University Hospital, told the crowd he talked with relatives in Beirut shortly before the rally began. "My mother was four blocks from the Commodore Hotel when it was hit by a bomb today," he said. "Is the Commodore Hotel a PLO stonghold?" The Commodore Hotel usually houses foreign journalists working in Beirut.

Dr. Rifka said his family is hungry, thirsty and feeling miserable. "This is not a rally, it is a funeral," he said.