Palestinian and Israeli forces exchanged intense artillery and rocket fire today amid continuing contradictory signals about progress in negotiations to avert an Israeli assault on West Beirut and send Palestinian guerrillas out of Lebanon.

Israeli forces stationed in the hills east of Beirut fired from tanks and heavy guns onto Palestinian positions and Lebanese civilian residential areas across a wide arc of West Beirut and its southern suburbs. The Palestinians fired on Israeli positions with Soviet-made Katyusha rockets and with artillery.

The intense new fighting and an apparent change of policy in neighboring Syria indicated to some observers that a plan for a political solution advanced by U.S. special envoy Philip C. Habib may be unraveling--or deliberately being subjected to new pressures.

According to the official Syrian news agency tonight, Damascus has rejected the idea of receiving Palestinian forces after they leave Lebanon. It said the Palestinians' place is in Lebanon until they can return to Palestine.

The agency quoted an unidentified government official as saying, "Syria in normal circumstances is a homeland for the Palestinians as well as to all Arabs. But under the present circumstances, there is no possibility of moving the Palestinian fighters from Beirut to Syria, because their normal place is where they are now, awaiting the return of their legitimate rights."

It was not immediately clear what caused the change from Syria's earlier reported acceptance of a plan to receive the guerrillas. Observers raised the possibilities of Soviet pressure, a Syrian demand for more financial compensation from Saudi Arabia or a desire to extract some concession from the United States.

Habib dispatched his assistant, Morris Draper, to Damascus, and Lebanese government sources said Draper would try to get Syria's approval to take in the guerrillas temporarily pending arrangements to disperse them to other Arab states, The Associated Press reported.

Today's flare-up between the Israelis and Palestinians followed the declaration in London by Farouk Kaddoumi, a senior Palestine Liberation Organization official, that an agreement to lift the Israeli siege of Beirut and move Palestinian forces out of the Lebanese capital was 70 percent completed and that it could be concluded in the next 24 hours.

This was contradicted by seemingly embarrassed PLO officials in Beirut, who said the only subject currently being discussed was a disengagement of forces.

The intensified shelling "is the best evidence that there's not all that much progress," one senior PLO official here said.

Kaddoumi also met with the British Foreign Office's second-ranking minister, marking an easing of London's stance toward the PLO. Details on Page A20.

The negotiating situation was made more confusing when a well-informed source close to Lebanon's Christian President Elias Sarkis said a four-point position delivered to Sarkis and Habib today from the PLO contained nothing about "their withdrawal," Washington Post correspondent Leon Dash reported from East Beirut.

What the source described as the most recent PLO position was brought to the presidential palace in Baabda this morning from Israeli-encircled West Beirut by Lebanon's Moslem Prime Minister Shafiq Wazzan. Wazzan had refused for the past week to cross into East Beirut to participate in the talks, demanding that Israel relinquish its control over the crossing points. The Israelis eased the blockade yesterday.

The source close to Sarkis said the PLO position that Wazzan delivered demanded a disengagement of the Israeli and PLO forces, the placement of an international military force to protect Palestinian refugee camps, the retreat of Israeli forces from around Beirut and discussions of future PLO-Lebanese relations.

Israeli forces invaded Lebanon June 6 with a major objective being the destruction of the Lebanon-based PLO as a fighting force.

According to state-run Beirut radio, shells landed at the two main crossing points between predominantly Christian East Beirut and the mainly Moslem western sector, where the Palestinian guerrillas and their Lebanese leftist allies are based.

The Beirut race track, Palestinian neighborhoods in West Beirut, the airport and the nearby Palestinian refugee camp of Burj Barajneh also were hit, the radio reported.

At least 10 members of a 50-man Lebanese security guard unit at the airport were reported wounded by shelling.

The Lebanese Defense Ministry issued a communique indirectly accusing the Palestinians of starting today's outbreak by shelling the Galerie Semaan crossing point between the city's eastern and western sectors to damage the negotiations.

That was the crossing used by Wazzan to go to Baabda in the Israeli-controlled hills southeast of Beirut for talks with Sarkis and Habib.

Afterward, Wazzan said he found it encouraging to be able to participate in such discussions, Beirut radio said. It quoted him as saying many obstacles still had to be overcome but that he hoped for concrete results soon.

In London, Kaddoumi, the PLO spokesman on foreign affairs, said the Palestinians were seeking a five-stage process for their withdrawal, but indicated they still had to agree on its timing and the makeup of an international peace-keeping force to oversee its implementation.

According to Reuter, Kaddoumi listed the steps as a cease-fire, disengagement of forces, deployment of the international force, Israeli withdrawal to five to seven kilometers (three to 4.2 miles) outside Beirut and withdrawal of Palestinian forces from the capital. Kaddoumi, in London as part of an Arab League delegation, said the agreement under negotiation applies only to Beirut and not to Palestinian guerrillas still operating in Israeli-occupied southern Lebanon, in northern Lebanon or in the Bekaa Valley in the east.

Kaddoumi said the PLO also was demanding that its guerrillas be allowed to take out all their weapons--heavy and light--when they leave Beirut, international guarantees for the safety of those Palestinians who remain in Lebanon and the application of Geneva Convention provisions on prisoners of war for the guerrillas captured by Israel.

Israel, which terms the guerrillas "terrorists," has said so far that it would not consider them prisoners of war, which would give them greater rights and protections.

Asked what the PLO was offering, Kaddoumi replied, according to Reuter, "All we have agreed is that we will leave Beirut to avoid the destruction of Beirut and an expected massacre of civilians."

Kaddoumi's statement marked the first time that a PLO official has spoken publicly about details of the negotiations.

His remarks seemed to catch PLO officials in Beirut off guard, creating more confusion than clarification about the guerrillas' real intentions.

A PLO official said privately that Kaddoumi was out of tune with Beirut--that he had "missed a cycle" and "didn't catch up with his instruction."

The official insisted that there was not even any agreement by the PLO to leave the country, only an agreement in principle to move its headquarters from Beirut, and that what this means would have to be negotiated with the Lebanese government once the Israeli pressure on the capital was removed.

The official said a "reduction of the PLO military presence in Lebanon is likely" but that "a PLO withdrawal is not being seriously contemplated."

The Palestinian news agency Wafa also was taking a hard line, dismissing foreign press reports about the PLO's "alleged evacuation." It said the PLO was "not going anywhere" until a number of specific conditions have been fully met and only as a result of "direct and detailed negotiations."

There was also considerable confusion about the obstacles still blocking an agreement.

Conflicting signals emerged about whether the PLO has dropped demands for keeping a political presence in Beirut once Palestinian guerrillas leave and for a U.N. framework for the international peace-keeping force that is supposed to ensure the Palestinians' safe withdrawal.

According to government sources, a key difference between Habib and the PLO involves the timing of the arrival of the international force. The PLO insists such a force should move into place before the guerrillas withdraw, while Habib has indicated this would take place afterward.

Habib also reportedly has rejected a proposed two-stage withdrawal.

The contradictions led some Lebanese analysts today to adopt a considerably more pessimistic outlook, fearing that the PLO still had not actually decided to leave and that an Israeli attack might come instead.