The government of Prime Minister Menachem Begin was stunned tonight by the U.S. decision to suspend the American-Israeli strategic cooperation agreement as a punitive measure for Israel's annexation of the Golan Heights.

After four days of confidently predicting that the United States would veto any U.N. Security Council attempt to impose sanctions and expressing assurances that the controversy over the Golan Heights issue would soon subside, Israeli officials appeared to be caught completely off guard by the U.S. move.

"We are not going to be ready to react until the Cabinet meets on Sunday to discuss it," said a government official who normally responds swiftly to the most subtle of shifts in nuance in U.S.-Israeli relations.

However, Associated Press quoted Israeli Ambassador Ephraim Evron in Washington as expressing "regret and deep disappointment." He said the United States was "hurting a friend" and giving "satisfaction to Syria, which is a surrogate of the Soviet Union" and added that the move will "encourage the extremist forces in the Arab world."

[Arab diplomats at the United Nations welcomed with skepticism the U.S. decision to suspend the strategic cooperation agreement, The Associated Press reported. "We welcome this as a signal from the United States to Israel, but we do not think it is adequate enough to generate pressure to deter Israel from its . . . expansionism," said Ambassador Clovis Maksoud, U.N. observer of the 21-member Arab League, in a typical comment.]

Until tonight, the Begin government had appeared sanguine about the world reaction so far to its annexation move Monday, with senior officials expressing confidence that Israel would be able to ride out the controversy.

"The negative reaction has been pretty much as we expected, and we took this into account when the decision[to annex]was made. But we hope and believe that the United States will prevent sanctions," David Kimche, director general of the Israeli Foreign Ministry, had said in an interview before President Reagan's Thursday press conference at which he condemned the annexation.

Other Israeli officials had expressed similar feelings of qualified relief at the level of international reaction, with one saying, "It's not as intense as one would think. There is some understanding of the strategic importance of the Golan Heights and the extremes to which Syria has been turning. We expect the reaction to subside eventually."

He added, "If sanctions are brought to the Security Council, our impression is that the United States won't allow it to pass."

The earlier upbeat mood in Begin's government, which had braced itself for a fiercer storm of world condemnation when the parliament voted Monday night to annex the Golan Heights, stemmed from what is being viewed here as several positive developments:

*Although France termed the annexation "unacceptable" and a violation of international law, Israeli officials in Paris were told that President Francois Mitterrand's scheduled Feb. 10 visit here will not be canceled or postponed.

*Although foreign ministers of the European Community, meeting in London, declared the annexation to be illegal and "invalid," a spokesman for the 10-nation body was reported to have said the issue would have no effect on European participation in the U.S.-sponsored Sinai multinational peace-keeping force.

* Despite the sharpness of official Egyptian statements against the annexation, it is obvious that Cairo's pique will not disrupt the peace process. Negotiations on Palestinian autonomy have continued at the subministerial level, and the two countries have signed a tourism agreement as part of the package designed to normalize relations.

* There is a perception among Israeli officials that there is something considerably less than unanimity in the Reagan administration on the question of the degree to which Israel should be rebuked.