Israel during the past 10 days has eased its conditions for pulling out of Lebanon, possibly setting the stage for achieving President Reagan's goal of the early withdrawal of all foreign forces from the country, according to Lebanese sources.

The sources, who declined to be identified, said Israel tentatively has agreed to a number of points, including compromises on its two main demands: normalization of relations and observation outposts in southern Lebanon.

According to the sources, Israel has tentatively agreed that it will moderate its demand to establish and man three to five observation posts in southern Lebanon after withdrawal of all foreign forces from the country. It also tentatively has agreed to postpone its insistence that the Lebanese sign a written pact normalizing relations between the two countries before withdrawal, the sources added.

However, in Jerusalem an official source who requested that his name be withheld said it was too early to talk about the imminent conclusion of an agreement, reported Washington Post correspondent Edward Walsh. More negotiations are necessary, the source said.

The source suggested that Israel was willing to be more flexible on the issue of normalization of relations if it could receive "temporary arrangements" that would amount to de facto normalization leading to a written agreement. The Lebanese sources indicated this could be achieved.

On the issue of Israeli troops manning observation outposts in southern Lebanon, the Israeli source's comments showed less readiness to compromise. He said that although U.S. envoy Philip C. Habib had come directly from Beirut to Jerusalem and held a 90-minute meeting Monday with Foreign Minister Yitzhak Shamir, there was no mention of a proposal that would adequately replace all the elements of Israel's observation post demand. However, Lebanese sources said a tentative compromise already had been worked out.

[After his meeting with Shamir, Habib said to reporters: "Maybe we have a solution, but I won't tell you."]

Rapid movement toward an accord in the long stalled troop withdrawal talks, which began Dec. 28, has come during shuttle diplomacy by Habib and while President Reagan and members of his Cabinet have openly applied pressure on Israel to come to an agreement, the sources said.

Lebanese sources credited Reagan with unblocking the talks and said they sense a marked new flexibility by the Israelis since Ariel Sharon was removed as defense minister on Feb. 14.

Moshe Arens, the new Israeli defense minister, "is a strong man and a little rude but he is a friend of America," said one Lebanese.

The sources were unwilling to speculate on when withdrawal might begin and they stressed that the issues tentatively agreed upon will not become final until a full accord is reached.

But, they said, there had been these tentative agreements:

* Israel has agreed tentatively to an undetermined period of months--a period of six is being talked about--after withdrawal to negotiate a formal normalization agreement. The Lebanese had insisted on a delay, fearing that if they made such an agreement now they would be subject to economic boycotts and additional pressures by other Arab countries. The Lebanese believe that Reagan will soon be able to get Jordan's King Hussein into peace negotiations, after which they feel they will be less exposed to charges of going it alone.

Israeli negotiators, however, are insisting on oral agreements for some limited trade and movement of persons across the Lebanese-Israeli frontier. The Lebanese have indicated they are willing to agree to that but appear not yet to be certain what arrangements they can make without offending other Arab countries.

* Instead of the residual Israeli force that Sharon had insisted stay behind to man security installations, the Israelis have agreed to joint Lebanese-Israeli inspection teams that would travel in Lebanese vehicles. The Israelis would not be garrisoned in Lebanon but would travel from Israel for the inspections.

* Lebanon's frontier with Israel will be guarded by Lebanese soldiers, including troops now in the Israeli-armed and -trained militia of renegade Lebanese Army major Saad Haddad. Haddad will retire from the military and give up his militia, but the Lebanese have agreed to treat him generously, perhaps by appointing him as a military attache to one of Lebanon's embassies.

* United Nations peace-keeping forces now posted five to six miles from Lebanon's border with Israel will be moved further north to assist the Lebanese Army in guarding the Palestinian refugee camps outside the southern Lebanon cities of Sidon and Tyre.

* Two active brigades of Lebanese soldiers would be stationed in the "security zone" extending above Lebanon's frontier with Israel, although negotiators have not agreed on the northernmost boundary of the zone.

In remarks recently, Reagan has said that the United States would be willing to help guarantee the security of Israel's frontiers, which many assumed meant he would deploy U.S. Marines there.

The sources said this was never a matter discussed in the negotiations here. They said Israel had rejected out of hand any multinational or U.N. force on its frontiers and that American negotiators had appeared not to be anxious to offer the services of U.S. troops.

They indicated that there will probably be the need for an expansion of the multinational force of U.S. marines and French, Italian and British troops now stationed in the Beirut area when Israeli, Syrian and Palestinian forces withdraw. But they said it has not yet been determined precisely where they would be deployed.

Ultimately, agreement by Lebanon and Israel hinges on whether the Syrians and Palestinian fighters will also agree to withdraw. The sources indicated that they have been given assurances repeatedly that they will do so and are hoping that they will live up to those promises.

"We are always afraid of a change in the mind of Syrians and Palestinians but we must presume their good faith," said one of the sources.

The Lebanese are clearly concerned about winning the assent of other Arab nations and not becoming isolated in the Arab world as did far larger and more self-sufficient Egypt after signing the Camp David accords.

The Lebanese economy, essentially a trader economy, is dependent on Syria as a trade route into the Arab world and on Saudi Arabia as its principal export market.

Fears were heightened here last week after Saudi Arabia imposed a ban on selected goods coming from Lebanon, alleging that they had originated in Israel. As the Lebanese see it, the outstanding issues to be resolved require a tough balancing act to achieve Israeli troop withdrawal and at the same time ensure against Arab world reprisals.

The next formal negotiating session between Israel and Lebanon is scheduled for Tuesday in the Beirut suburb of Khaldah.