President Reagan sought to calm Israeli fears about the possibility of U.S. arms going to Jordan by writing Israeli Prime Minister Menachem Begin yesterday that "I am determined to see that Israel's qualitative technological edge is maintained."

The president said that Defense Secretary Caspar W. Weinberger, who on Saturday completed a 10-day swing through Saudi Arabia, Oman and Jordan, "brought me no new request" from Jordan for American arms.

"Any decision on future sales to Jordan or any other country in the region will be made in the context of my administration's firm commitment to Israel's security and the need to bring peace to the region," Reagan said in his letter released by the White House.

He said, "Recent press reports have presented incorrect and exaggerated commentary regarding U.S. military assistance policies for the Middle East."

David R. Gergen, White House communications director, said the president was referring to those press accounts of the Weinberger trip that claimed the administration was redirecting its military policies from Israel to Arab countries.

Gergen said Pentagon spokesman Henry E. Catto Jr. had told the White House that no one on the Weinberger plane could recall talking about such a redirection.

The problem began when a Weinberger deputy on the plane was explaining to reporters how recent events, such as the assassination of Egyptian President Anwar Sadat and the attempted coup against the pro-western government of Bahrain, had changed the Pentagon's attitude about what constituted the biggest threat to Middle East countries.

Internal subversion and pressures on moderate governments by Moslem extremists now looked like a bigger threat than a direct Soviet attack, the official said.

Asked at that point if the administration had redirected its policies to conform with this changed threat assessment, the Pentagon executive paused, then answered in the affirmative, stressing he was talking only about "military policies," not the whole spectrum, which is the business of the State Department.

As part of the Pentagon's response to the new threat assessment, Weinberger and other defense executives are trying to strengthen U.S. ties to nations in the Middle East, Persian Gulf and Africa.

Weinberger said repeatedly during his trip that this was his mission, that the United States needed many friends in those areas along with Israel. At no time in talking with reporters traveling with him did Weinberger talk about punishing Israel. Also, the often quoted remark about not letting Israel hold the United States "hostage" was not made by Weinberger but by a deputy who was making the point that the administration thought that Weinberger should go forward with his twice-postponed trip to the three Arab countries even though Israel might have hoped for different timing.

Weinberger did, in fact, mention on his way to Jordan that he would be discussing the possibility of selling Jordan mobile Hawk missiles and perhaps the F16 fighter, but stressed no decisions had been made on those weapons. The thrust of his remarks was that it would be against the strategic interests of the United States to let a strong military relationship develop between Jordan and the Soviet Union.

Other officials on the Weinberger plane held out little hope of talking King Hussein of Jordan out of accepting $200 million worth of Soviet mobile antiaircraft missiles, partly because the United States could not match the bargain-basement price.

Weinberger repeated on the NBC "Today" show yesterday that "what is important is that the United States have more than one friend in the Mideast," that any deal for selling Hawk mobile missiles or F16s to Jordan is "a long way down the road," and, if consummated, he contended it would not jeopardize Israel's military superiority.

Begin, in a letter to Reagan that the president had not received before issuing his own, said mobile Hawks and F16 fighters would put Israel "in direct, real and severe danger . . . . If those sophisticated weapons are to be supplied to Jordan, just as similar ones already have been committed to Saudi Arabia, what will become of the qualitative and quantitative edge you were so kind to promise me to maintain that Israel might better deter aggression and prevent war, which is what all of us so deeply seek?"