Syrian soldiers encircled Palestine Liberation Organization positions in eastern Lebanon today, blocking movements of guerrillas loyal to PLO Chairman Yasser Arafat and turning away shipments of arms and ammunition to them.

Rebels claimed yesterday that they had taken eight strategic PLO positions in the Bekaa Valley. Two key aides to Arafat disputed that today, however, saying the rebels had captured only two to four positions, but they claimed that after the battle yesterday, Syrians increased their checkpoints around PLO positions in eastern Lebanon and installed dissidents to man checkpoints along the road in the area.

"We're still in the Bekaa," said Ahmed Abdel Rahman, Arafat's chief spokesman. "We're still in Baalbek, but they took the roads."

The PLO military chief, Khalil Wazir, known as Abu Jihad, said rebels helped the Syrians in identifying Arafat loyalists and routinely disarmed them today if they attempted to move from their positions.

He said that the Syrians were permitting food to pass through their lines but they either seized or turned away arms and military cargo intended for the loyalists.

Today's developments complicated further the situation within the PLO, where elements of Arafat's main Fatah organization have launched a challenge to Arafat's leadership, saying he is leading the guerrilla movement away from its main goal of confronting Israel.

The reining in of the PLO appeared to strengthen the bargaining position of Syrian President Hafez Assad in the tangled and potentially explosive Lebanese situation, but it humiliated restless PLO guerrillas and Arafat's top aides, who spoke today of possible counterattacks against Syrian troops if the noose is not loosened.

"We will defend ourselves," said Rahman in an interview this morning at the Baddawi Palestinian refugee camp in northern Lebanon's port city of Tripoli, where Arafat and key aides have gathered since suffering setbacks in other areas at the hands of PLO dissidents--who they say were aided by Syrian tanks.

"We must wait for a while, for it is not an easy thing to open fire on our brothers in the Syrian Army," Rahman said. "We want to be brothers in one front against the Israelis and we do not want to open a front against each other."

The government-run press in Syria denied today that Assad's forces had played any role in the intra-Palestinian conflict, although it reported declarations of anti-Arafat units as the PLO split boiled over into an all-out shoot-out.

Anti-Arafat rebels also denied Syrian involvement today, saying the fire fight was only a counterattack to prevent Arafat loyalists from blocking their supply routes.

"We threw his forces back and reopened our supply routes," the rebel leader, Capt. Said Musa, known as Abu Musa, said today. "We threw them back very far."

Wazir charged that Syrian field officers in Lebanon told him that while they had not aided the rebels, one of their officers had disobeyed higher command. The Arafat aide said he did not accept this explanation, however, and indicated that he believed the orders to assist the dissidents had come from Damascus.

Here and in Tripoli there was anger at Syria today for what Arafat's loyalists described as its tank shelling to help rebels in the predawn fighting yesterday in which dissidents seized Arafat's positions. His aides said at least seven loyalist fighters were killed in the skirmishes because the PLO refrained from returning the Syrians' fire.

"We have an order from Arafat not to clash with Syrian troops," a loyalist said here today, "but I think our fighters will not accept it."

The PLO also said Syrians have captured 30 loyalist troops and two battalion commanders but released them today.

The tight Syrian ring around the PLO, evident in a quick tour of PLO operations in the Tripoli area and into the Bekaa Valley today, diminished the importance, at least for the moment, of the PLO wild card in the Lebanon deck. It fortified Assad, who has blocked resolution of the Lebanese occupation issue or any overall U.S. peace effort in the Middle East.

Assad, with entrenched military positions in Lebanon, has condemned the Israeli-Lebanese peace agreement and has refused to leave Lebanon until Israel is forced to abandon the agreement and depart unconditionally.

The PLO, fearing that President Assad is preparing to make a deal at its expense, has threatened to draw the Syrians into a wider war with Israel by conducting hit-and-run guerrilla operations through Syrian lines.

The tight Syrian security in the Bekaa today included checkpoints every mile, at which identification and notice of destination were required. It seemed to indicate that Assad is not eager to be associated with attacks on Israelis from his lines.

Arafat's aides expressed the hope that the supportive telephone call Arafat had from Saudi Arabia's King Fahd and the urgent appeals to Arab leaders would resolve the conflict in their favor, but there was doubt among them.

The latest twist in the PLO's fortunes has led to speculation that less than a year after his U.S.-arranged evacuation from Beirut, Arafat intends to reestablish a base in Lebanon. His aides deny that, even as headquarters operations in the camp here and the two in Tripoli are enhanced.

But Arafat's spokesman denies that he is reestablishing operations in Tripoli, where opposition to the presence of the Syrian Army is strong.

Asked where Arafat's base is now, Rahman said, "He flies like a bird from tree to tree because he's facing more than one enemy."