Robert C. McFarlane, President Reagan's new Middle East special envoy, concluded two days of talks with Israeli officials here today at the outset of a diplomatic mission that appears to have become bogged down over remaining differences between Israel and Lebanon.

McFarlane, who came here from Beirut and returned to the Lebanese capital later today, is spearheading a renewed U.S. effort to win Syria's agreement to withdraw its forces from Lebanon, a condition Israel is insisting on before it withdraws its troops.

But according to Israeli officials, the bulk of McFarlane's meetings here dealt with Lebanese fears that Israel's plans for a partial pullback of its troops in Lebanon could lead to the de facto partition of the country between Israel and Syria.

Israeli radio said tonight that McFarlane asked the Israelis to provide a definite timetable for their complete withdrawal from Lebanon in return for pledges that Syrian and Palestinian forces also would leave. The report said Prime Minister Menachem Begin, although initially opposed, was now willing to consider the idea.

McFarlane met this morning with Begin and later held his second session in two days with Foreign Minister Yitzhak Shamir and Foreign Ministry Director General David Kimche. While here he also met with Defense Minister Moshe Arens.

Following his meeting with Begin, McFarlane told reporters his discussions with Israeli officials were "extremely worthwhile."

McFarlane, Reagan's deputy national security affairs adviser, was appointed special Middle East envoy last month, replacing Philip C. Habib, whom Syrian officials had refused to see in connection with the troop withdrawal stalemate. McFarlane's arrival here this week came as something of a surprise, since it had been widely assumed that he would go to Damascus first for talks with the Syrians, who are willing to see him.

But it soon became clear that Israel's current "redeployment" of its forces to lines along the Awwali River north of Sidon remains a major concern to the Lebanese and an issue that McFarlane apparently felt had to be dealt with first.

The Israeli government, under domestic pressure because of continuing casualties in Lebanon, announced last month that its forces would withdraw from the outskirts of Beirut, the Beirut-to-Damascus highway and the Chouf Mountains southeast of Beirut to presumably more defensible positions along the Awwali.

During a visit to Washington in late July, Arens and Shamir received the Reagan administration's official blessing for the redeployment, which both sides agreed to describe as only the first stage in the total withdrawal of all foreign forces from Lebanon.

However, the Israelis have vowed to remain in southern Lebanon as long as the Syrians are in the country, giving rise to fears that the withdrawal stalemate could easily slide into a partition of Lebanon.

"Lebanon still suspects the redeployment will lead to the impression of partition," an official said after McFarlane held his first session with Shamir yesterday. He said Shamir reiterated Israel's intention to leave Lebanon as soon as the Syrians also withdraw, and said the foreign minister offered to hold direct talks with the Lebanese on the issue.

The official said that before going to Damascus McFarlane "wanted to straighten out this problem."

It was not clear today at the conclusion of McFarlane's talks here whether the U.S. envoy had succeeded in this, allowing him to turn his attention to the Syrians. It was also not clear exactly what the Lebanese are seeking from the Israelis in connection with the redeployment, under which Israel expects the Lebanese Army to take over many of the positions it evacuates.

[Israel released 10 Syrians from the Ansar prison camp in southern Lebanon Thursday and handed them over to Syrian authorities, an Israeli military spokesman said. The Syrians, captured more than a year ago during Israel's invasion of Lebanon, were released for medical and humanitarian reasons, Reuter quoted military sources as saying.]