Secretary of State George P. Shultz said yesterday that the resolution adopted by the Arab League summit could be a "genuine breakthrough" in the search for Middle East peace if it implies Arab willingness to recognize Israel.

However, Shultz, in testimony before the Senate Foreign Relations Committee, cautioned that it still is unclear whether the plan made public yesterday by Arab leaders in Fez, Morocco, contains an implicit recognition of the Jewish state's right to exist.

He was referring to language in the resolution stating that the U.N. Security Council should "guarantee peace among all states of the region" including an independent Palestinian state. The resolution does not mention Israel by name; but, as Shultz noted, that language could be interpreted to mean tacit recognition of Israel since it is a state within the region.

"There might be an implied recognition of Israel," Shultz told the committee. "I hope that is so. If that's what it is, then it's a step forward. It may not sound like much, but it would be a genuine breakthrough . . . and very, very important."

He also noted that "key elements" of the Arab plan are "at variance" with President Reagan's Mideast initiative, which calls for the Israeli-occupied West Bank and Gaza Strip to be granted eventual self-rule "in association with Jordan."

Most of the Fez resolution runs directly counter to Reagan's proposals. But administration officials said privately it should be viewed not as an Arab rejection of the U.S. initiative, but as the opening move from the Arab side in a potentially long and intricate diplomatic process that the United States hopes will lead to Jordan joining the negotiations over the future status of the occupied territories.

Specifically, the officials continued, they believe the Fez resolution represents a maximum position that the Arab countries intend to use for further probes of whether the Reagan initiative shows promise of opening the way to new negotiations capable of resolving the Palestinian question in a manner acceptable to the Arab world.

The officials were especially encouraged at the inclusion of the language about guaranteeing peace among all states of the region. When Saudi Arabia proposed a plan with similar language for consideration at an Arab summit in Fez last November, radical Arab objections caused the meeting to break up before it formally got under way.

The fact that governments representing both moderate and radical Arab opinion have agreed on such language in responding to the Reagan initiative is regarded here as a potentially significant gesture and signal by the Arab world that it wants to explore the chances for new negotiations under American leadership.

A further sign of that intention, the officials added, was the relative absence of any harsh anti-American rhetoric at the Fez meeting.

Underlying this view is the belief of administration policy makers that, in the wake of the Palestine Liberation Organization's expulsion from Beirut, the Arab countries are increasingly receptive to a fresh try at breaking the impasse over the West Bank and Gaza and that the situation can be channeled toward an eventual Arab endorsement of Jordan entering the Camp David talks.

The Fez plan reaffirmed the longstanding Arab position that the PLO is the "sole and legitimate representative" of the Palestinian people, and it called anew for the occupied territories to become an independent Palestinian state.

But, U.S. officials, stressing their view that is part of a maximum bargaining position, are hopeful that Fez will turn out to be the start of a process that will see the Arab states gradually back away from the weakened and fragmented PLO and give Jordan's King Hussein a green light to enter the peace process as agent for the PLO and the Palestinian people.

The officials cautioned that it will take several months before they have a clearer idea of whether this can be done. However, they are known to believe that Hussein is receptive to the idea if he can get sufficiently broad backing within the Arab world and if the United States can induce Israeli Prime Minister Menachem Begin's government to show more flexibility in its approach to negotiations.

Shultz referred to that goal obliquely yesterday when he told the committee, "The big question is whether it will be possible to broaden participation in the peace process. If it is, then we have something going for us. If it isn't, then we don't."

In his second appearance on Capitol Hill in two days, the secretary acknowledged that Israel and the Arab League have made "initial formal reactions" to the Reagan initiative that either oppose the president's plan outright or that are "at variance with our proposals."

But he also reiterated the administration strategy, which U.S. officials privately describe as refusing to take "no" for an answer, and pressing ahead in an effort to change the Israeli and Arab attitudes.

"The opening positions have been announced," he said. "We will be working hard over the next few weeks in light of the new dynamic the initiative introduces to bring the peace process forward. I pledge that we will be exercising the creativity, the persistence and the dogged determination to succeed . . . . "

In a related development, Defense Secretary Caspar W. Weinberger, speaking after the last of 800 Marines left Beirut after helping to oversee the PLO evacuation, praised the U.S. forces for the "flawless handling" of their mission and said: "I am absolutely delighted nothing did go wrong."