Israel today accused Syria of allowing Palestinian guerrillas to replace the bases they lost in southern Lebanon and Beirut this summer with new strongholds behind Syrian lines in the Bekaa Valley of eastern Lebanon.

In a communique issued to explain today's heavy Israeli air attacks on Syrian and Palestinian positions in eastern and central Lebanon, Israel's military command said there are 4,000 to 5,000 guerrillas operating in the area and accused them of 98 cease-fire violations since late July.

"The Syrians are enabling the terrorists to cross lines and are supplying them with intelligence information concerning Israeli deployments and giving them logistic support," the communique said. "The terrorists are operating . . . with Syrian knowledge, protection and full consent when they go to attack our forces, and Israel cannot agree to this."

According to the communique, since late July, 12 Israeli soldiers have been killed, 20 wounded and nine captured as a result of cease-fire violations. The communique suggested that a bazooka attack that killed three Israeli soldiers on Friday was the immediate cause of today's air assault.

"The terrorists are establishing a new deployment of forces in the Bekaa to replace their strongholds in Beirut and in southern Lebanon," the military announcement said. "They are deployed in the eastern sector of the Bekaa in the area of Baalbek, Mar Elias and the town of Yanta. There are terrorists in the villages as well as in the open areas."

Today's air attacks were the heaviest over eastern and central Lebanon since July 22, when Israeli planes pounded Syrian and Palestinian positions in response to what were termed "constant violations" of the cease-fire.

Military sources said today's strikes destroyed five Palestinian command posts, plus artillery positions, rocket launchers, armored vehicles and one Soviet-built SA9 ground-to-air missile battery. Most of the targets were Palestinian, although some Syrian Army positions were also hit, they said.

There were no Israeli losses in the attacks, the military command said.

The attacks followed a warning by the Israeli Cabinet yesterday that Israel will not tolerate a "war of attrition" with Syria in Lebanon and was prepared to use "diplomatic or military means to achieve this end."

Israeli officials reiterated today that this was the only "political message" meant by the air raids. "From our point of view, we are not interested in fighting Syria and we hope this message will be understood," the officials said.

Officials said that today's attacks were meant as a renewed warning to Syria, which Israel has said repeatedly it holds responsible for Palestinian guerrilla activity, and not the beginning of renewed general fighting in eastern Lebanon. But in a speech delivered while the air assault was going on, Israeli Foreign Minister Yitzhak Shamir suggested that Israel will maintain pressure on Syria to agree to a withdrawal of its forces from Lebanon.

"After we settle matters with Syria -- everyone knows what is happening and may happen in the coming days -- the border problem will become much smaller," Shamir said. "Israel will leave Lebanon as soon as possible together with all the foreign forces that will leave it. We have no other conditions."

Shamir emphasized that a peace treaty between Israel and Lebanon is not a condition for Israeli withdrawal. He also said that even after a troop withdrawal Israel would be satisfied with less than a formal, signed peace treaty with Lebanon so long as there is an adequate "security arrangement" protecting Israel's northern border.

This statement appeared to be a backing off from recent Israeli attempts to put pressure on Lebanese President-elect Bashir Gemayel to sign a peace treaty with Israel.