Buoyed by the severe setback delivered to President Reagan's Middle East peace initiative this week, Israeli officials have begun speaking with great optimism about the prospects for a troop withdrawal agreement with Lebanon.

"Everybody has the impression we are reaching the end of the negotiations," a senior official said today. "We all have the impression that we are within reach, and it's not a matter of too much time."

Another source familiar with the negotiations said he saw reason for the Israelis' optimism.

"They are very close," he said. But he added that unless there is agreement on the key issue of the future role of Saad Haddad, a former Lebanese Army major long allied with Israel, old issues that have been put aside in the talks could be revived and the entire agreement jeopardized.

The one cloud in the Israelis' optimistic mood of the moment centers on Reagan's recent announcement that the United States will not deliver 75 F16 fighter-bombers to Israel until the Israelis withdraw from Lebanon.

Although the planes are not due to be sent here until 1985, this is said to have caused deep anger in the Israeli government as an "unbearable" linkage of arms supplies with political demands.

In his first television interview as defense minister last night, Moshe Arens called Reagan's declaration "an unprecedented statement in the 35 years of Israeli-U.S. relations."

"It has never happened that a president has said that the offer of aid is conditional on any political concessions," Arens said. "Today it is Lebanon, tomorrow it may be in another area."

Arens said Reagan's position on the F16s "requires us to make a reassessment of our arms purchase policy," and other officials spoke of a need for Israel to become more self-sufficient in terms of arms.

A serious move by Israel away from dependence on U.S. arms supplies is considered unlikely here for the near future, however. The Israeli arms industry is large and sophisticated, but officials here concede that it is years away from being able to produce aircraft such as the F16 and F15.

On the issue of Haddad, Israel has been emphasizing for weeks its demand that he be given a "command role" in a security zone to be established in southern Lebanon as part of a troop withdrawal agreement. Lebanon has agreed that Haddad's Israeli-supplied militia can remain in southern Lebanon but has balked at providing an important role for Haddad, who faces longstanding treason charges in Lebanon for forming his militia and establishing an independent enclave along the Israeli border.

The source said both Israel and Lebanon appear adamant in their positions regarding Haddad and that concessions on the issue will have to come at "the highest level" of the two governments.

Israeli officials say they base their optimism on indications of Lebanese willingness to discuss some kind of role for Haddad in southern Lebanon and on what they perceive as renewed U.S. attention to the Lebanon talks now that King Hussein of Jordan has announced he will not enter broader peace negotiations based on the Reagan plan.

"The Americans are now more interested in a settlement in Lebanon per se than a settlement in Lebanon as a corridor to something else"--progress on the Reagan plan, the Israeli official said.

The Israelis have long maintained that the United States unnecessarily complicated the task of achieving a troop withdrawal by introducing an overall proposal for a Middle East peace settlement involving the Israeli-occupied West Bank and Gaza Strip.

At the same time, skeptics have suggested that Israel has had an incentive to prolong the negotiations with Lebanon to ensure that the Reagan initiative, which was rejected out of hand by Israel, remained moribund. Hussein's decision to break off his talks with Palestine Liberation Organization Chairman Yasser Arafat and bow out for now from any negotiating role on the future of the West Bank and Gaza came as a great relief to the Israelis. They were especially pleased that both the Jordanian government's announcement of Hussein's decision and Secretary of State George P. Shultz's comments put the onus for failure on Arafat and the PLO leadership.

Officials here say they expect continued U.S. diplomatic efforts along the lines of the initiative Reagan outlined Sept. 1. But they also say they expect the United States to adopt a "more cautious, traditional role" in Middle East diplomacy, including "full consultation" with Israel on every step.

Officials here speak in terms of "the Reagan plan as such" being dead.

Meanwhile, Israeli military authorities announced that an Israeli soldier was killed and two others wounded today in an ambush of their bus near the southern Lebanese city of Tyre.