The Israeli warplanes that bombed Iraq's nuclear plant Sunday flew a pattern seemingly designed to evade detection by American AWACS planes patrolling the skies over Saudi Arabia, U.S. officials said yesterday.

They added that the Iraqi plant would not have become operational until at least mid-July, a few weeks after Israeli elections set for June 30, and that it would have taken two years, under a crash program, to produce bombs at the Iraqi plant.

Last year, these officials said, U.S. intelligence estimated it would be 1985 or 1986 before Iraq could produce nuclear weapons under a normally paced program.

These and other detailed revealed yesterday are expected to be explored as the Reagan administration and Congress study the intelligence and foreign-policy implications of Sunday's attack.

The eight F16 bombers and six escorting F15 fighters did not fly into Iraqi airspace at high altitude, as some reports have said, but stayed close to the desert floor, well-informed officials disclosed.

They said this was to foil the radars aboard the AWACS (airborne warning and control system) planes as well as those on the ground in Saudi Arabia, Iraq and Jordan.

The Israeli jets streaked over Baghdad at an altitude of a few hundred feet, dropped 2,000-pound bombs on the nuclear plant about 12 miles southeast of the city, and then zoomed high into the sky for an escape through Jordanian airspace, the officials added.

The jets came in low, they said, in order to hide amid the clutter that snows the scopes of ordinary radars when they try to find objects close to the ground. AWACS planes based in Saudi Arabia were focusing on Persian Gulf approaches to the north at the time of the raid, according to the Pentagon.

The combination of ground clutter and distance kept the Awacs from detecting the Israeli raiders, according to officials who have been trying to determine if there was a U.S. intelligence gap.

Although officials did not say so, it is possible that Israel knew the routes and schedules of the four AWACS planes in Saudi Arabia and planned Sunday's raid accordingly. Israel is well-acquainted with much of the technology aboard the Boeing AWACS, in part because it has its own sophisticated warning planes, the Grumman E2C Hawkeye, supplied by the United States.

The Israeli escape route saved fuel and put more miles between the returning planes and the AWACS to the south in Saudi Arabia, sources said. Flying over Jordan, rather than taking a dogleg route around it and over Saudi Arabia, saved hundreds of miles and kept the Israeli planes farther north of the AWACS.

Flying home at high altitude, probably about 40,000 feet, increased the risk of radar detection but saved fuel. Planes burn considerably more fuel when flying through the bumpy air near the surface of the earth.

Jordan's radar detected the Israeli planes racing home through its airspace but the Jordanians made no attempt to scramble fighters or to shoot the Israeli jets down with missiles, according to reports from Arab capitals. t

U.S. government analysts sifting through reports from Baghdad said yesterday that there is no sign of a retaliatory strike being prepared.

Looking at the raid from Israel's perspective, U.S. specialists theorized yesterday that it marked a victory for Israelis pushing or a preemptive military policy -- striking before Israel can be struck.

Although the Reagan administration announced on Wednesday that it will hold up today's scheduled delivery to Israel of four new F16s from the General Dynamics plant in Fort Worth, Tex., this suspension may be short-lived.

It is still unclear what more, if anything, the administration will do in response to Israel's using American-supplied planes to carry out its strike.

Asked yesterday what the pentagon told general Dynamics about delivering the four F16s, a defense spokesman said the company was told to hold off "until further notice."

In Tel Aviv, Israeli Prime Minister Menachem Begin told reporters attending a diplomatic reception that Defense Secretary Caspar W. Weinberger had recommended to President Reagan the cutting off of U.S. economic and military aid to Israel as a way of protesting the bombing raid.Secretary of State Alexander M. Haig Jr. opposed that course, Begin said.

"The man who emphatically demanded to withhold from us all economic and military aid and to halt our supplies is none other" than Secretary of Defense Weinberger, United Press International quoted Begin as saying.

Last night, the Pentagon issued this response in Weinberger's name: "I am sorry Mr. Begin is proceeding on erroneous assumptions. I have made no such recommendations."