The Reagan administration is expected to drop plans to include 40 additional F15 combat aircraft in the new arms sales package for Saudi Arabia that Congress will soon consider, according to congressional and State Department sources.

U.S. officials said the decision reflected mounting congressional opposition to the administration's plan for major new arms sales to Jordan and Saudi Arabia.

Together with two squadrons of F16s or F20s and mobile Improved Hawk antiaircraft missiles for Jordan, the F15s for Saudi Arabia are the most controversial items in two packages the administration is putting together for the two Arab nations.

"As of now, we have made a decision not to advance any Saudi request for aircraft," one official remarked.

"It was a judgment on what's sustainable up on the Hill," another official added.

A denial of the longstanding Saudi request for more F15 aircraft would constitute the first time Washington, long the principal arms provider to the Saudi kingdom and particularly its air force, has spurned King Fahd on a major weapons item.

The United States has already sold the Saudi Air Force 62 F15s, more than 100 F5s and five Airborne Warning and Control System (AWACS) aircraft.

The decision could have adverse repercussions on the U.S.-Saudi military relationship, resulting in the Saudis' buying either the French Mirage 2000 or the Tornado made by Britain, Italy and West Germany.

Both France and the consortium have been campaigning hard in the kingdom for the sale of their warplanes, but the Saudis have been awaiting the outcome of their request to buy more F15s.

White House spokesman Larry Speakes insisted Friday that no final decision has been reached "in regard to the specifics on arms sales" to either Jordan or Saudi Arabia.

But two administration officials who briefed Senate staff members last week on the results of an interagency study on U.S. arms transfer to the Middle East and Persian Gulf reportedly promised that the forthcoming arms package for Saudi Arabia will not include any combat aircraft, according to one aide.

One State Department official said it is still possible the Saudi F15 request would proceed as a separate item after Congress has resolved the contentious Jordanian arms issue and dealt with the less controversial sale of more Sidewinder air-to-air missiles, Stinger ground-to-air missiles and other military equipment to the Saudis.

The Saudis have interpreted a letter delivered to King Fahd last Dec. 6 by Defense Secretary Caspar W. Weinberger, pledging strong support for Saudi security, as a promise the United States would sell the additional F15s.

Saudi sources said that the administration subsequently had informed them of a delay because of the Middle East arms review begun in January, but assured them that the aircraft would be supplied eventually.

A briefing on the study given to three House committees in July argued strongly in favor of continued arms sales to the Saudis because "Saudi Arabia is the only country in the Gulf region which is both friendly to U.S. interests and capable of playing an important regional role."

It also said "our willingness to meet their defense equipment requirements is recurring proof that we mean what we say about our vital interest in Saudi Arabia and Gulf security."

When the Carter administration first proposed selling 62 F15 fighters to Saudi Arabia in the late 1970s, Israel and its supporters in Congress strongly opposed the sale and argued that the sophisticated jet would be a serious potential threat to the Jewish state in the event of another Arab-Israeli war. The original deal was only narrowly approved, 55 to 44, by the Senate after acrimonious debate.

A condition for congressional approval of the first F15s was a Saudi promise not to base them at Tabuk air base in the northwestern corner of the kingdom and within easy range of Israel. The Saudis have kept that promise but have reportedly flown the aircraft in and out of Tabuk from time to time.

The Saudis are known to be shopping for an advanced aircraft to station at Tabuk to replace their obsolete British-made Lightning aircraft now based there. Both the British and French have the advantage over Washington of being able to offer an advanced aircraft without any similar legislative restrictions being placed upon their sale. Either the Mirage 2000 or Tornado could be based at Tabuk.

U.S. proponents of the F15 sale, including some administration officials, have long argued that Israel would be better off if the Saudis continued to buy U.S. aircraft because Washington would have more leverage over their use and basing in the kingdom.

The French company, Dassault-Breguet Aviation, was reported in the European press last spring to be close to clinching a deal for the sale of 46 Mirage 2000s in return for Saudi oil.

But the oil barter deal has never been concluded, partly because the company was willing to accept only roughly 50 percent of the cost in oil and wanted the rest in cash.

For its part, British Aerospace, with strong help from the British government, has been trying to persuade the Saudis to purchase 20 European-made Tornado jets and 26 Hawk trainer/fighters. British Secretary of Defense Michael Heseltine has made three trips to the kingdom over the past year, partly in connection with this possible sale.

The Saudis have made no final decision on which of the three competing planes to buy. Partly, it seems, they have been awaiting the outcome of their request for more F15s.

Some analysts also believe they have delayed a decision because of the large budget deficit facing the kingdom this year -- $20 billion or more -- due to the drastic reduction in its oil exports, recently little more than 2 million barrels a day. However, the kingdom still has massive reserves, somewhere in the neighborhood of $100 billion, that it could dip into to buy new aircraft.