Israel now has a fleet of highly sophisticated warning planes, complete with crews trained in the United States, to help offset the coming loss of the Sinai Desert, which has served as a buffer zone.

These planes, the fourth of which was delivered by the United States to Israel last month, are part of a modern arsenal that is expected to grow in the wake of the Camp David agreements.

Defense Secretary Harold Brown plans to travel to Jerusalem and Cairo in January to discuss with his counterparts the requests for additional American weaponry. Pentagon officials said it would be the first such trip by a U.S. defense secretary. Brown had announced his intention to make the trip before the Camp David summit.

Both Israel and Egypt had submitted long wish lists of American weaponry to the Carter administration before the peace agreement was reached and are expected to argue now that the loss of the Sinai buffer zone makes their requests more urgent than ever.

President Carter during the Arab-Israeli peace negotiations committed the United States to putting up the money for two new Israeli air bases in the Negev Desert to make up for the ones to be lost by returning the Sinai to Egypt.

Pentagon spokesman Thomas B. Ross said yesterday that the bases probably will cost between $300 million and $1 billion. Those estimates are "vary preliminary," Ross added.

"We would compenstate the Israelis for their withdrawal" from their Sinai air bases at El Arish on the northern coast of the desert and at Ezion at the head of the Gulf of Aqaba, Ross said. He said Israel probably will build the new bases.

As for items on the Israeli wish list, Ross said yesterday that the Carter administration is "proceeding with consideration" of the 10-year, $13.5 billion package already on file. "There has been no change," he added.

Both Israel and Egypt hope to get more Amercian tanks, armored personnel carriers and antiarmor weapons to beef up their infantries. Pentagon officials said Egypt, in contrast to Israel, which is now stronger militarily than ever, is still woefully weak in both its air and ground forces.

The 50 F5E fighter-bombers Carter has promised to deliver to Egypt, even if they went against Israel in concert with the 60 F15 fighters going to Saudi Arabia, are not considered by Pentagon specialists as any match for the sophisticated Israeli air force.

The new warning planes Israel had received from the United States under a $170 million deal provide an extra degree of aerial superiority. No foreign country has this plane, the Grumman E2C Hawkeye.

Carrying two pilots and a crew of three to operate the sophisticated electronic equipment, the Hawkeye could detect with its radar an enemy fighter 150 to 200 miles away.

Other equipment aboard the Hawkeye would tell the crew the course and speed of the enemy plane, information that would be sent in code to commanders on the ground so they could order fighters aloft.

Other sophisticated electronic equipment on this warning plane includes a passive system that can detect another plane's radar emission from about 400 miles away.

Each of the four Hawkeyes, which have just joined the Israeli air force, is designed to direct fighter plane attacks against 30 different enemy aircraft while keeping radar track of hundreds of others.

Stepped up aerial patrol plus ground monitoring stations like the ones now in the Sinai are expected to be part of the Israeli military response to the shrunken borders agreed to under the new framework for a peace agreement.

However, Carter administration officials insist there is no intention of putting any kind of American military presence in Israel. Israel Prime Minister Menachem Begin told the Senate Foreign Relations Committee yesterday that, despite no provisions for such bases in the peace agreements a U.S. military would be welcome.

Sen. Frank Church (D-Idaho), summarizing Begin's testimony yesterday, told reporters that the Israeli prime minister had said, "We would be welcome at Haifa if we wanted to establish a naval installation there. We would be welcome in the Sinai, if we were interested in establishing an air base there, of course, with the permission of the Egyptians. . ."