In an effort to get an Arab arms sale through Congress, the Reagan administration is preparing to seek approval to sell Saudi Arabia a package of missiles worth more than $300 million, according to administration and congressional officials.

The package, said to include Sidewinder, Stinger and Harpoon missiles, may be sent to the Capitol within the week, some sources said. But others suggested that the White House may not give final approval to the proposed package at this time because of concerns that it would repeat the political fight that forced the administration last month to postpone a $1.5 billion arms sale to Jordan indefinitely.

The proposed Saudi missile package is being split off from a larger $1 billion Saudi request -- which includes helicopters and upgraded electronic warfare gear for its F15 fighter planes -- in the hopes that it will be less controversial to congressional supporters of Israel, the sources said.

One senior State Department official said the administration will argue that the missile package simply adds to supplies of ammunition the United States has already sold the Saudis. Saudi Arabia needs the new missiles because of the increased threat to the northern Persian Gulf by Iran's latest offensive in its war with Iraq, he said. "We have no interest in seeing the Saudis run out of ammunition trying to defend the northern gulf from Iranian attack."

Congressional supporters of Israel, led by Sen. Alan Cranston (D-Calif.), however, have said they will oppose any arms sale to Saudi Arabia because of claims that the Saudis give moral and financial support to Libya and the Palestine Liberation Organization and have not helped U.S. efforts toward a Middle East peace plan.

Cranston has said he is considering an effort to try to block the delivery this June of five AWACS radar-warning planes approved by Congress in 1981 after a bitter fight on the Senate floor.

In the final push to get Senate support for the $8.5 billion AWACS package, President Reagan pledged that before the planes were delivered he would send Congress a certification that "significant progress" toward peace in the Middle East had been accomplished "with the substantial assistance of Saudi Arabia."

State Department officials have said they are preparing papers certifying the Saudis' help to the peace process.

Even though the Saudis want the missile package because of the Iranian threat to Kuwait, one source said, the delivery of the AWACS is a higher priority. And the Saudis want to be sure the administration will push hard for any proposed arms sale, rather than withdraw without a fight as it did on the Jordan sale, the source said.

The numbers of missiles in the proposed package could not be learned yesterday.

A spokesman for the American Israel Public Affairs Committee, a major pro-Israel lobbying group, said one proposal under consideration would sell the Saudis nearly 1,000 more advanced Sidewinder air-to-air missiles, giving them a higher number of missiles per plane than the U.S. Air Force or any NATO country. The spokesman said his group will oppose the sale on the grounds the Saudis don't need great numbers of new weapons.