Two U.S. Airborne Warning and Control Systems (AWACS) jets arrived today after an 11-hour flight from their base in Oklahoma to provide Egypt's new president, Hosni Mubarak, with a concrete symbol of U.S. support for his government.

The planes with the electronic saucers on their backs were said to have arrived as Mubarak announced his 31-member Cabinet, which was virtually the same as that of his slain predecessor, Anwar Sadat.

Mubarak, who assumed not only the presidency but the premiership yesterday, decreed in the first Cabinet session that the death penalty would be invoked for anyone using unlicensed weapons. The move was the first in a series of expected measures to try to stem the growth of Islamic extremist violence of the sort that led to Sadat's assassination last week.

The attention in Egypt during the first full day of Mubarak's presidency, however, focused on the arrival of the U.S. radar planes. Announcement in Washington that the AWACS would be immediately deployed here was greeted with satisfaction by the Egyptian government, which said the real reason for the planes' arrival was to patrol its tense western border with Libya.

Egypt made plans to receive the two jets with maximum publicity, presumably to draw the public's attention to the extent of U.S. support.

In what appears to have been another case of fumbled signals between Washington and Cairo, however, a planned full-blown public greeting for the planes never took place.

The two jets, Egyptian officials had announced, were to land and be based at the Egyptian Air Force's sprawling Soviet-built Cairo West air base.

The Egyptian Ministry of Information organized buses for foreign and local reporters to see the planes land. The base commander, Gen. Ahmed Nasser, organized a small honor guard of red-braided military policemen on the tarmac. As the assemblage waited for the planes' arrival, the base commander even ordered one of his air crews to take a U.S.-made fighter aloft for the benefit of the television cameras.

At noon, when the planes had been expected to land, the word circulated that the AWACS had entered Egyptian airspace and would soon be at Cairo West. However, apparently on orders from the U.S. military, they were diverted to another "undisclosed" Egyptian base.

About 1 p.m., a smiling Nasser gathered the hundred or so waiting journalists and said there had been a "change of plans" -- the AWACS on entering Egyptian airspace had gone on patrol immediately and would not land until midnight.

A U.S Embassy spokesman, queried about Nasser's assertions that both AWACS had been put on immediate duty without even landing and with their crews unrested, indicated that the AWACS had not actually begun flying missions yet.

While here to attend Sadat's funeral, Secretary of State Alexander M. Haig Jr. met with Mubarak, Foreign Minister Kamal Hassan Ali and the defense minister, Gen. Abdel Halim Abu Ghazala, to promise continued U.S. support.

As a result of these meetings, Haig announced the expansion of previously planned joint military maneuvers in Egypt's western desert next month and agreement to step up deliveries of previously contracted military hardware. He also hinted at new commitments of support for Sudan.

After such declarations in Cairo, however, Egyptian officials have been puzzled by later State Department clarifications when Haig returned to the United States.

"We are glad for the American statements of support," said one Egyptian Foreign Ministry official. "But what we can't understand is why we are told the United States is going to do one thing, and then we are told that it is not exactly so and it only said it would take the matter under advisement."