Yigael Yadin's Democratic Movement for Change decided today to reopen negotiations on joining Prime Minister Menachem Begin's coalition government.

Although Yadin emphasized that the decision does not signify a decision to join the government, members of both Yadin's party and Begin's Likud Party consider that the chances are better than even that the Movement will eventually join. Hard bargaining is ahead, however.

A Movement communique recommended that negotiations be "short and efficient," but even if Yadin's group does not join the government before the prime minister leaves for the United States next week, the resumption of talks is seen here as strengthening Begin's hand in his coming meetings with President Carter.

The comparatively dovish Democratic Movement would lend an aura of moderation and international respectability to Begin's hardline. Likud party and his right-of-center religious party coalition partners. Moreover, the Movement's additional 15 seats would considerably strengthen the slim majority of the present government, which holds 63 seats in the 120-member Parliament. The Movement could also lessen Begin's dependence on the conservative religious parties.

The Democratic Movement broke off negotiations with Begin and the Likud three weeks ago Begin went ahead and formed a coalition with two religious parties, but left three Cabinet seats open should the Movement decide to join.

The Movement's communique said the decision to "reopen negotiations at this state, even when many serious subjects are still in disagreement, was made because of good will and a feeling of national responsibility . . ." A member of the party's secretariat, Eli Eyat, said in an interview that, although Begin's trip to the United States was not mentioned in the communique, today's meeting made it clear that the Movement wanted to strengthen Begin's position with the Americans "even though we disagree completely with some aspects of his foreign policy."

The Movement believes that Israel should make territorial concessions on the occupied West Bank in exchange for a real peace with the Arabs, while Begin's Likud Party is committed to keeping the West Bank under Israeli control.

"We feel that we will be able to moderate the day-to-day policies of the government," Eyal said.

The feeling of wanting to band together in the face of American pressure typifies the mood in Israel at the moment, even among many of Begin's political opponents. Eyal said that if the talks fail, no announcement will be made until Begin's return from Washington.

The Movement's secretarist and Parliament members voted 14-6, with 3 abstentions, to reopen negotiations. Yadin, after delivering a report on his latest "clarification" talks with Likud and religious party leaders, voted with the majority.

Yadin said Likud offers had created "new conditions that were not present in the past." He warned, however, that it will not be easy to get the changes the Movement wants in the negotiations.

According to the communique, the Movement had asked Begin to clarify several points. One was Begin's offer to allow the Movement to speak freely in Parliament and to vote against the government on matters of foreign affairs and defense.

This concession was designed to overcome the party's reluctance to join the government because of Likud's hawkish policies. In practice, however, it would be difficult for the Movement to vote against a government in which it is a member, and the present Likud coalition has a majority in any case.

Although many points still must be negotiated, it seems clear that the Movement, if it decided to join the government, will have to join more on Begin's terms than might have been the case earlier. Begin's Likud Party controls most of the important ministries and he has shown that he can put together a government without the Democratic Movement.