The Reagan administration would look "sympathetically" at a request by Israel or any other friendly country to have American troops stationed within its borders, Defense Secretary Casper W. Weinberger said yesterday.

The new defense secretary, in his first news conference at the Pentagon, stressed that he did not expect Israel to make such a request and therefore was talking about a hypothetical situation. His remarks suggested nevertheless that the Reagan administration is swinging away from the post-Vietnam policy of sending American money but not troops to distant crisis areas.

Israeli officials have said they will not ask for American troops to fight for them but would allow Israeli territory to be used as a staging area for U.S. troops pursuing Washington's own interests.

On the other controversial questions, Weinberger indicated he would be sympathetic toward deployment of the so-called neutron bomb in Europe, and toward giving Saudi Arabia equipment to extend the reach and firepower of its U.S.-built F15 fighters.

After declaring that "the basic policy is that we don't go where we're not wanted," Weinberger said of the Reagan administration: "We would always examine very carefully and sympathetically requests for the stationing of American troops in countries where they were desired."

As for Israel specifically, Weinberger said that "I can't conceive of there being any situation," in which Israel would request U.S. troops. "If it were requested by Israel," continued Weinberger in discussing a hypothetical American troop presence there, "we would certainly examine it very sympathetically and very carefully."

He said at another point in his news conference that the same kind of requests coming from other Middle Eastern countries would be viewed sympathetically as well. Taking pains to find the middle ground between Arab and Israeli interests, Weinberger recalled that the United States looked sympathetically at Saudi Arabia's request for American early warning aircraft after the Iranian-Iraqi war broke out.

Weinberger made these other points in his news conference:

Neutron warhead -- "I think the opportunity that this weapon gives to strengthening theater nuclear forces is one that we very probably would want to make use of." President Carter postponed deploying the weapon that U.S. military commanders contend would kill enemy troops without causing as much damage to the surrounding countryside as present-day nuclear weapons would. Weinberger said that he thought it was "wrong" for the Carter administration to change course on deploying the enhanced radiation warheads in Europe.

Saudi F15 fighter planes -- "We want to make them as effective as we can" for Saudi Arabia. The Saudis want extra fuel tanks and armament racks to make their F15s more lethal. Weinberger did not commit the administration to going along with that request but did say that the Saudis have "a difficult defense problem with a long coastline and a small number of forces and immensely valuable resources for the free world." Partly in response to Israeli objections, the Carter administration promised Congress that the F15s going to Saudi Arabia would be armed only for defensive, not offensive, operations.

MX land missile -- Weinberger said that he was still examining alternative ways for basing his new ICBM for fear that lawsuits would "slow down and ultimately even stop" the weapon from being deployed in the valleys of Nevada and Utah as the Carter administration envisioned. One alternative under study, Weinberger said, is putting the big missile on old surface ships that could be scattered around the oceans to make them hard for the Soviets to target. This scheme "would require very little time and very little cost," he said. But no decisions on alternatives have yet been made.

Gen. David C. Jones, chairman of the Joint Chiefs of Staff -- Weinberger said that President Reagan has not yet decided whether to keep Jones as chairman. The general has another 18 months to go in his term.