Carter administration policy makers believe the peace offer Israeli Prime Minister Menahem Begin made public yesterday will launch "a process" of significant bargaining with Egypt.

"Of course it is not acceptable to the Arabs in its present form," one American planner said. But "the hopeful sign," he said, "is that Begin is willing to keep the ball rolling," and Egyptian President Anwar Sadat has indicated his willingness to respond

Becuase the United States has played a middle-man role in transmitting information between Sadat and, Begin, administration officials believe they can discern what will be repromise between Egypt and Israel. But it will require "hard bargaining," said one U.S. specialist, and "there is an awfully long way to go."

On its face, there would appear to be a standoff on the core dispute: Sadat's demand for "self-determination" and ultimately a "Palestinian state" for the Arabs on the Israeli-occupied West Bank of the Jordan River and in the Gaza Strip, versus Begins offer of "self-rule" for the Arbswith a continued Israeli military presence in these regions.

If American officials are not miscalculating the domestic political support that Begin can obtain for further negotiating flexibility, however, they anticipate extensive give-and-take from the present Israeli and Egyptian bargaining positions.

They see these positions "as openers," in diplomatic terms, although the declared objectives may never change.

U.S. specialists who have helped work out three previous limited military disengagement plans in the region since the 1973 war - two between Israel and Egypt, and another between Israel and Syria - say they are not dismayed by the task ahead.

These planners see two central problems for Sadat in the existing Israeli plan.

One obstacle is Israeli insistence on maintaining Israeli military forces for security in the West Bank-Gaza "administrative autonomous entity." A second major obstacle is the ambiguous nature of the "reexamination" of the plan that Begin wants permitted at the end of five years.

To Sadat, Israel's desire for a continuing military presence on the West Bank - and Begin's failure to specify what transition may be possible after five years - both imply continued Israeli domination of the "automomous" region, thereby making the proposal unacceptable.

What is possible in the first instance, U.S. experts suggest, is a variation that would satisfy Israel's security requirements while making the plan tolerable to the moderate Arabs. This might be a mixed Israeli-Arab security force, or internationally manned early warning posts and supplementary forign troops, in varying combinations.

The security problem for Israel in the West Bank-Gaza region, American specialists noe, is primarily not the danger of Arab invasion, but rather the problem of terrorism and subversion.

Begin, speaking in the Israeli Parliament yesterday, did not say that Israel would never withdraw its military forces from the West bank and Gaza, specialists noted. He said Israel would never abandon these areas to "the control of the murderous organization that is called the PLO," the Palestine Liberation Organization.

Similarly, American specialists noted, Begin deliberately left open what would happen to the autonomous region at the end of five years. This leaves the road of diplomacy open, diplomats pointed out, for negotiations to try to bridge the gap between Sadat's call for Palestinian "self-determination" and begin's offer of "self-rule."

What must be remembered, American sources underscored, is that Sadat has not committed himself to negotiating a detailed solution of the Palestinian question that will resolve that issue.

On the contrary, Sadat has said that Egypt can only seek to establish the principles for settling this wider issue. Sadat said other Arab nations, such as Jordan, Syria and Lebanon, will each have to negotiate their own detailed peace agreements with Israel.

What Sadat requires is only enough agreement with Israel on the Palestinian issue to avoid exposing Egypt to charges that it "sold out" other Arab nations to satisfy its own selfish interest. Even this is no easy goal to achieve, however.

Sadat claims that he virtually has in hand, out of his Ismailia meeting with Begin, the separate agreement that would return Egypt's captured territory in the Sinai. Sadat in an interview on Tuesday said this represents a major "leap forward," meeting Egypt's essential requirements.

The specifics of this military agreement, which will consist of a phased Israeli withdrawal, are yet to be worked out, as begin emphasized yesterday.

In sum, American officials maintain in private that the possibility now exists for developing from the existing Egyptian-Israeli positions a plausible compromose.