Authoritative Lebanese government sources said today that the U.S. State Department was premature in reporting this week that Lebanon had agreed to enter direct diplomatic talks with Israel on withdrawal of foreign forces from this country.

The sources declined to say whether Lebanon was seeking some concession from Israel in return for starting such negotiations, but the comments suggested that negotiations were not going as smoothly as the United States might like. Diplomats speculated that the Lebanese government might be waiting to announce the talks with Israel until it has been able to gauge whether strong opposition is likely to materialize among the Moslem population at home or elsewhere in the Arab world.

Prime Minister Shafiq Wazzan, a Moslem, has stressed that Lebanon still was using Washington as an intermediary in talks with Israel on a troop withdrawal, even though Israel would like direct talks as a prelude to establishing normal diplomatic relations with the country.

"The contacts going on . . . are not conducted by Lebanese authorities directly," Wazzan told reporters last night after a Cabinet meeting.

Syria currently has more than 30,000 troops in Lebanon and Israel approximately twice that figure while there are estimated to be 10,000 Palestinian guerrillas.

U.S. envoy Morris Draper, who will conduct talks aimed at a troop pullout agreement, arrived here today after a three-day delay while he rested in London with a kidney ailment.

Draper was expected to travel from here to Jerusalem and then to Syria in his shuttle. In those capitals he faces a key problem: Israel says it will pull out simultaneously with Syria after all the Palestinian guerrillas have departed first, whereas Syria says it will not leave until all the Israelis are out.

Senior Lebanese officials say that Lebanon essentially will accept any plan that the United States can develop that would obtain a complete withdrawal of the foreign forces. As a first step to get negotiations started, Lebanon is seeking partial pullbacks of Israeli troops from around the Beirut area.

A political columnist for the respected newspaper An Nahar today contended that Israel was the principal barrier to an agreement on withdrawal because of its insistence on a variety of conditions difficult for Lebanon to accept. In particular, he cited Israel's insistence on integration of the Israeli-trained and -supplied militia of former Lebanese major Saad Haddad into the regular Army to police southern Lebanon and for movement toward normalization of relations with Lebanon.

One diplomat here said that Secretary of State George P. Shultz may have set the goal of clearing out foreign forces by the end of the year as a method to keep pressure on Israel to negotiate.

The Lebanese government sources confirmed that the government was considering a proposal to add one or more civilians to a joint Israeli-Lebanese military committee that has handled routine contacts between the armies since last summer. Newspapers here have given prominent coverage to reports from the United States that Lebanon and Israel might hold talks with diplomats in this way within the week, but the government has not issued a public response to such reports for a second day.

Prime Minister Wazzan reaffirmed the Lebanese government's position that it particularly is seeking a withdrawal of Israeli troops, which invaded the country on June 6.

"Our basic priority in our daily work is following up on the issue of withdrawal, and especially Israeli withdrawal," he said. President Amin Gemayel has said that a simultaneous pullout of all foreign forces is acceptable despite the emphasis on an Israeli pullback.

In other developments here:

* Israel withdrew its forces from the outskirts of two mountain villages southeast of Beirut, leaving the Lebanese Army alone to keep peace between feuding Moslem Druze and Christian Phalangist militias.

* Palestinians living in the Ayn Hulwah refugee camp outside Sidon set fire to a tent put up by U.N. relief workers as temporary housing in a protest demanding permanent homes.

* The Christian Phalangist radio station reported that a senior official of the Palestine Liberation Organization escaped an assassination attempt four days ago in the eastern Bekaa Valley. The report provided no details on the alleged attack against Khalil Wazzir, also known as Abu Jihad.