Defense Secretary Caspar W. Weinberger agreed today that the United States will buy $100 million worth of Israeli products in the last three months of this year to help offset Israeli purchases of U.S. military equipment, U.S. and Israeli sources said tonight.

Weinberger and Israeli Defense Minister Yitzhak Rabin were expected to announce the results of their meetings Wednesday, and U.S. spokesmen declined to discuss them tonight. But knowledgeable sources said that officials from the two countries were close to working out a modest memorandum of agreement aimed at strengthening the Israeli economy by aiding its military and high technology industry.

Weinberger's pledges, which will also include encouraging Israeli sales to U.S. military bases in Europe and the Mediterranean, are part of a larger U.S. effort to help the new Israeli government cope with its crippling economic problems. The Weinberger efforts, however, appeared to be separate from ongoing discussions of whether the United States will allow Israel to postpone debt payments and whether the administration will substantially increase the amount of direct aid to the Jewish state.

Weinberger's chief spokesman, Michael I. Burch, confirmed yesterday that the defense secretary will fly to Amman on Wednesday for dinner with Jordan's King Hussein. The pros and cons of such a visit have been privately debated for more than two weeks and plans were only finalized tonight.

Burch declined to discuss the purpose of the trip, but other officials said the United States is worried about Hussein's interest in purchasing new Soviet weaponry. Jordanian officials, who believe that Washington has not been forthcoming enough in weapons sales, have previously bought Soviet-made SA8 missiles, anti-aircraft guns and radar, officials here said. Hussein has privately informed U.S. officials that he is now considering larger purchases.

In addition, Weinberger is eager to keep Jordan involved in the Middle East peace process and did not want him to feel snubbed while the defense secretary visited Israel, one official said.

Weinberger's decision to buy $100 million worth of Israeli products temporarily takes the place of an earlier agreement that expired Oct. 1 and called for U.S. companies to buy Israeli goods worth 15 percent of Israeli military purchases in the United States. The new three-month agreement, if carried out for a year, would double the percentage to 30 percent, but officials stress that negotiations will continue on a longer term agreement that is unlikely to be quite so generous.

U.S. officials also said they will work to remove various impediments to Israel's bidding for contracts to supply U.S. military facilities overseas.

Said an Israeli official: "The idea is to help us by strengthening our economy, not just by throwing money at it."