A Syrian-sponsored plan to halt a five-day battle for control of three Palestinian refugee camps between Shiite militiamen and Palestinian guerrillas faltered today as the guerrillas dismissed it and Lebanese gunmen besieging them vowed to fight to the finish.

Militiamen of the Shiite Moslem Amal movement appeared to have edged forward in tightening the noose around Palestinians holed up in the heart of the Sabra and Shatila camps south of Beirut. However, the persistent sound of tank shells, rocket-propelled grenades and machine-gun fire this afternoon at the northernmost entrance to the shantytowns indicated that the battle was continuing.

Meanwhile, the Damascus-based Popular Front for the Liberation of Palestine said today that Palestinian guerrillas have formed suicide squads "to inflict the heaviest losses possible" on the Moslem militiamen attacking the camps.

The Popular Front, a Marxist-oriented group, described reports of agreement to the Syrian-sponsored truce as "baseless and aimed at lowering the high morale of our heroic fighters." Political sources said Amal had approved the plan.

Police reported that casualties from the five days of fighting have risen to 240 killed and about 1,000 wounded. Many bodies have not been recovered from the besieged camps yet, however.

The newspaper An Nahar quoted French Embassy sources as saying two French residents of Beirut were abducted Wednesday, United Press International reported, raising to 10 the number of western kidnap victims missing in Lebanon, including five Americans.

Black smoke billowing at a distance from a nearby gas station, where Lebanese Army soldiers milled about nervously near their armored personnel carriers, confirmed morning reports of combat behind the Arab University and in the Fakhani neighborhood. Tank shells resounded through the narrow, empty streets leading to Sabra from the northeast.

An Army soldier said there had been some fighting at the station. "Now we are in full control here. There are a few guerrillas inside. We'll take care of them in no time," he said.

A group of Amal militiamen guarding another western passageway into Sabra through the ruins of the sports stadium and an unfinished but damaged wrestling hall barred reporters from entering. Sniper bullets rang through the deserted buildings.

A group of militiamen wearing black bandanas walked wearily out of an alley. Asked whether they had allowed access to any Red Cross ambulances today, one gunman looked over his shoulder and said: "We have not let them in and we will not let them in." Since the fighting started Monday only two brief medical rescue operations have succeeded.

At an Amal office in the seafront slum of Ouzai, Haidar Salloum, an area officer of Amal, ruled out the chances of a peaceful solution to the Shiite-Palestinian conflict, in which the Shiites are seeking to prevent Palestinian guerrillas from reestablishing themselves as a force in Beirut or in southern Lebanon.

"There is no settlement. It can only end militarily. It's not going to stop just like that," said Salloum when asked for his view of the Syrian-drafted cease-fire proposal.

The Syrian-sponsored plan calls for an immediate cease-fire and entrusts the Lebanese Army's mainly Shiite 6th Brigade with security of the camps and the collection of weapons from Palestinian guerrillas still inside. The 6th Brigade has been helping Amal battle the Palestinians, who have responded with hit-and-run attacks and surprise ambushes.

Eyewitnesses said today they saw Lebanese Army tanks enter the camps followed by bulldozers. Residents in neighborhoods adjacent to Shatila said they had heard dynamite explosions all day today and suspected that houses were being blown up. Burning tires were thrown around certain sections of the camps in a bid to smoke out Palestinians still inside.

Military sources said a number of soldiers were wounded when a rocket hit one of their tanks, knocking it out of commission.

When asked why Amal had not succeeded in flushing out the guerrillas from Sabra and Shatila, Salloum replied: "It is their area; they know all the streets and underground tunnels. They come out from where we least expect them to. But we will fight them to the last minute."

An elaborate underground network of passages and hiding places served as an effective bomb shelter during Israeli aerial raids in 1982. The guerrillas had stored food, ammunition, fuel and medical supplies there. Palestinian sources said there was a secret tunnel leading from Shatila to Burj al Barajinah, the largest of the camps under attack, which used to house 25,000 refugees.

The cover provided by shelling from Palestinian positions in the Druze-held hills around Beirut has helped guerrillas hold their ground inside the camps. A warning by Druze Cabinet minister Walid Jumblatt's Progressive Socialist Party "against the use of the areas under its control as a base for operations aimed at striking at the agreement that was reached in Damascus" went unheeded.