The Reagan administration, facing stiff congressional resistance to its planned $1 billion arms sale to Saudi Arabia, tentatively is offering to withdraw 1,600 Maverick antitank missiles from the package in hopes of making the deal more palatable to critics.

Informed sources said yesterday that the administration is trying to determine whether congressional concern about threats to Israel's security will be assuaged if President Reagan delays the $360 million Maverick sale indefinitely.

The sources stressed, however, that the idea is being discussed informally and that a decision has not been made.

On June 11, Reagan withdrew a proposal to sell the Mavericks after it became evident that Congress would vote overwhelmingly to block the deal. When it became known last month that the administration was considering resubmitting the sale as part of a larger package, opponents warned that it would touch off a major new test of strength between the White House and the Democratic-controlled Congress.

The sources said the plan being pressed by the administration in informal talks with Congress gives priority to sale of 12 F15C and F15D jet fighters to serve as replacements for Saudi planes that crash or wear out in the next few years.

In return, the administration reportedly would promise not to provide the Saudis with the F15E, a greatly improved model that will replace earlier versions of the F15.

The administration also would agree to freeze the "in-country" Saudi force of F15s at 60 by keeping most of the so-called "attrition aircraft" in the United States and sending them to Saudi Arabia only as they are needed as replacements.

According to the sources, the tentative plan to emphasize sale of the F15s was dictated by desire to keep the Saudi air force at maximum strength during Persian Gulf tension resulting from the Iran-Iraq war.

In addition, manufacture of the earlier-model F15s will be phased out next year, and the administration, which estimates that the Saudis will need several replacements beginning in 1990, must act soon if the planes are to be built.

The sources said intensive administration lobbying with Congress and American-Jewish groups was to be assessed at a White House meeting yesterday by senior officials from the State and Defense departments, the National Security Council staff and the Office of Management and Budget.

They added that the meeting was expected to produce a recommendation for Reagan and his top advisers.

The sources said the administration viewpoint has been divided between officials, centered in the State Department and the Pentagon, who believe that U.S. credibility with the Saudis requires pushing the sale even at the risk of losing, and a more politically oriented faction, including White House chief of staff Howard H. Baker Jr., that wants to spare Reagan a possibly humiliating legislative defeat.

The sources said the administration's tentative view is that the opponents still have sufficient votes to block the sale but that concessions under discussion probably would swing enough votes to keep the opposition from overriding a veto.

If that analysis holds, some sources predicted, the administration is likely to make its move in early October to have sufficient time for required consultations before the end of the congressional session, which could come in November.

In addition, the sources said, the administration tentatively envisions selling electronic equipment to improve the older-model Saudi F15s' flight and combat capabilities; better computers and gun barrels to upgrade 150 M60A1 tanks to the level of newer models, and a new type of ammunition feeder for the Saudis' M109 self-propelled artillery.

However, the sources noted, these items are regarded as less important than the F15s and could be removed from the package if the administration decides that such a move would win more support for the plane sale.

The sources said a potentially complicating factor is the administration desire to sell 70 shoulder-fired, ground-to-air Stinger missiles and 14 launchers to the tiny gulf state of Bahrain.

Saudi Arabia has Stingers. But the sources said many members of Congress are wary of introducing more into the volatile gulf region and, as part of the negotiations on the Saudi deal, are arguing that the administration should reconsider selling them to Bahrain.Staff writer David B. Ottaway contributed to this report.