Secretary of State George P. Shultz said today he will visit the heads of government in Saudi Arabia, Syria, Lebanon and Israel to make a new personal assessment of the troubled Middle East, but he cautioned that he sees no real prospect of an immediate breakthrough toward the withdrawal of foreign forces from Lebanon.

Speaking to reporters as he prepared to begin his hastily improvised mission Monday, Shultz indicated that the central focus of his trip will be on Syria, which has emerged as the stumbling block to troop withdrawals from Lebanon and the center of inter-Arab politics in its efforts to fracture and dominate the Palestine Liberation Organization.

Shultz will hold talks in Damascus with Syrian President Hafez Assad, who has refused to meet with U.S. special envoy Philip C. Habib in his current efforts to implement the troop withdrawal agreement brokered by Shultz on a visit two months ago.

"At this point we don't have a reading of the Syrian situation, and so we very much want to get one," Shultz said.

Damascus radio said Shultz would face "increased Syrian determination" to reject the withdrawal of its troops from Lebanon, Reuter reported.

As the hurried preparations were being made for Shultz, six senior Palestinian mediators met with Syrian Foreign Minister Abdul Halim Khaddam Sunday in an effort to end the violent mutiny in the PLO, Reuter reported from Damascus. The team also met with rebel leaders there. Story on Page A24.

Shultz's plans to stop in the Middle East appeared to have caught many officials there by surprise, and it was not immediately clear in what order he would visit the countries or how long he would be staying, according to Washington Post correspondents Herbert H. Denton in Beirut and David B. Ottaway in Jerusalem.

Arrangements for Shultz in Beirut reportedly began being made by Habib and other U.S. officials late Saturday afternoon, Denton reported.

Shultz will go first to Saudi Arabia, where senior aides said the discussions planned with King Fahd are likely to center on Syrian attitudes and activities and on the possible Saudi role in producing a change of heart in Damascus.

Since Shultz's last trip to the Middle East, Syria has shown no sign of willingness to remove its forces from Lebanon in parallel with the Israelis.

The other major development since Shultz's last trip has been the outbreak of fighting within Fatah, the main faction of the PLO, over the leadership of PLO Chairman Yasser Arafat and Syria's expulsion of Arafat from Damascus after he accused Assad of aiding the rebels.

Habib is to meet Shultz Monday in Saudi Arabia and may accompany the secretary of state during his tour, which is likely to last most of the week. Shultz said that, at this point, he has no plan to shuttle between various capitals as he did two months ago in arranging the final terms of the Israeli-Lebanese agreement.

Shultz would not say whether Habib has been able to produce any positive steps in his recent talks in the area. According to officials in Shultz's party, the United States--through Habib--had been seeking agreement in Israel and Lebanon to some new proposals that would lend greater urgency and incentive to Syria to agree to withdrawal from Lebanon. One idea that had been under consideration was the setting of a "date certain" for Israel's withdrawal conditional on Syrian withdrawal.

"Everything comes slow and hard in the Middle East," Shultz told reporters in discussing his trip.

Meanwhile, the official Syrian news agency reported that Assad sent a cable to President Reagan, congratulating him on the occasion of America's Independence Day, according to Reuter. The agency did not release the text.

In Beirut, diplomats said it was a significant act since the Syrian official media for weeks have been attacking the U.S. role in the Israeli-Lebanese troop withdrawal accord.