Syria poured fresh troops into areas of Lebanon today to quell a rash of killings in the mountain villages southeast of here avenging the assassination Wednesday of Moslem leftist Kamal Jumblatt.

At least 200 Christians have been killed over the past two days by members of Jumblatt's Druze sect, an 11th Century offshoot of the Moslem religion. Syrian officials fear that the killings could plunge Lebanon back into civil war.

That fear was echoed today by the Rev. Antonios Khreish the partriarch of the Maronite Christian church, who called the killings "massacres."

"I have warned and I am warning again," he said, "that violence will only lead to violence."

Druze Moslems adn Maronite Christians, who lived peacefully side-by-side in the Chouf mountains during most of Lebanon's 19-month civil war, have a long history of fighting each other.

According to Maronite officials here, at least 7,000 Christians have fled their villages near Jumblatt's home in the mountain town Moukhitara. About 700 of these went today to the presidental palace in Baaba, a suburb of Beirut to demand government protection.

Syrian officials have told diplomats here they are not afraid of violence breaking out in Beirut, despite the killing of about a dozen people since Wednesday and scattered gunfire last night and today.

They are fearful, however, of the situation in that mountianous Chouf area, with its long history of violence and the Druze tradition of exacting revenge.

Syrian troops in battle dress, supported by tanks and artillery, moved into the Chouf today to secure these villages. According to reports here, at least 40 persons were arrested, including a parliamentary supporter of Jumblatt, Zahir Khatib. He was considered the most radical member of Jumblatt's small parliamentary group.

Christian officials here, who warned their followers against escalating the violence, said enraged Druze fighters had begun their chain of killing before the Syrians arrived.

One family lost 23 members when the Druze dynamited the church in which they had taken refuge, security forces said.

Despite the violence against the Christians, there is no evidence that they had anything to do with the machine gun killing of Jumblatt. Security forces have said nothing about who may have been responsible, and Jumblatt is known to have had a myriad of personal, political and religious enemies.

Jumblatt's son Walid, 26, who was installed yesterday to replace his father as leader of the Druze sect, also appealed for an end to the revenge slayings.

"I call on you to be true to my father's memory and testament by upholding your fraternal relations with your neighbors," he said in a statement broadcast tonight by the national radio.

While the Syrians tried to stem the revenge killings, there was intense speculation over who would succeed Jumblatt as the national leader of the Lebanese Moslems.

"He was the only national figure the leftists could call their own. Now they have no one," said one observer of Lebanese politics.

To underscore this point, one Lebanese Moslem commented today, "We cried for Jumblatt. We wouldn't have done that if they had killed Saab Salam," former prime minister and an old-time Moslem political leader.

Referring to Jumblatt, he said, "he took care of us during the war. No one else did."

Jumblatt's death illustrates the vacuum in Lebanon's Moslem political hierarchy.

While the Christians are represented by at least three strong national political figures - Camille Chamoun, Pierre Gemayal and Suleiman Frahjieh - as well as President Elias Sarkis, there are no comparable leaders on the Moslem side.