The Reagan administration, fighting to save its proposed sale of sophisticated radar planes to Saudi Arabia from congressional veto, has sent its new ambassador, Richard W. Murphy, to make a new try at winning Saudi agreement to greater U.S. participation in the operation of the aircraft.

Murphy, a career diplomat who was confirmed by the Senate Friday, left for Saudi Arabia Monday, and informed sources said yesterday that he carried a proposal aimed at reversing the Saudi government's adamant resistance to obligatory inclusion of U.S. military personnel in crews of the Airborne Warning and Control System (AWACS) planes.

Although they refused to give specifics, the sources said the plan being conveyed by Murphy represented a new variation of the joint-crewing proposals the administration has been making to the Saudis in hopes of staving off almost certain congressional defeat of the $8.5 billion aircraft sale.

While it was not clear whether they traveled together, Murphy's trip was made in conjunction with the temporary return home of the Saudi government's principal representative here, Prince Bandar bin Sultan.

Murphy also was accompanied by Air Force Maj. Gen. Richard V. Secord, who had a major role in working out the sale of the AWACS planes and other advanced aircraft equipment.

The sources said Murphy's mission marked an almost last-gasp attempt to move the Saudis from their refusal to accept a compromise on the control issue that could overcome strong opposition to the sale in both houses of Congress.

The deal will be blocked if both houses vote against it within 30 days of receiving formal notification of the sale. That is scheduled to go to Capitol Hill today.

Until now, the sources conceded, the Saudis have refused to consider the idea of obligatory joint crewing, and some sources said Bandar's return home was intended as a signal from the ruling royal family that it is not interested in further negotiation.

The Saudi position, according to these sources, is that it still wants to buy the AWACS planes and other equipment, but only under terms of the sales package as it stands.

In the Saudi view, these sources said, it is up to President Reagan to decide whether to go forward with the deal and, if they fail to get the AWACS planes, they have made clear to Washington that they are prepared to turn to the Nimrod radar plane system being developed by Britain.

In describing Murphy's mission, administration sources said they do not expect any dramatic, overnight turnabout. Instead, they contended, the hope is to initiate a dialogue that could lead to an acceptable compromise before Congress votes on the sale.

As of last night, administration officials said publicly and privately that Reagan intends to go ahead with the notification to Congress on schedule today despite the almost universal feeling in congressional circles that the package, as it now stands, is destined for defeat.

In private, though, they said the timetable might be changed if Murphy's talks with the Saudis produce results that might make delay advisable. As of last evening, however, they insisted that there had been no developments of that sort.

In addition, the officials said some thought was being given to delaying notification until Thursday, when the Jewish New Year holiday ends. The original plan to send the notification yesterday was put off because it would have come on the first day of the two-day Jewish holiday.

The officials also insisted that the notification, when submitted, will include the AWACS planes as well as range-enhancing fuel tanks for F15 jet fighter-bombers the Saudis have on order, air-to-air Sidewinder missiles and aerial refueling tankers.

They noted, however, that if it is decided later to separate the AWACS planes from the package, notification will have to be withdrawn and resubmitted to Congress in revised form. graphics: photo. Richard W. Murphy: reportedly carried a proposal aimed at reversing Saudi objections to plan.