President Reagan said yesterday that "it seems as if some progress has been made" in the agreement of Jordan's King Hussein and Palestine Liberation Organization chairman Yasser Arafat, and others in his administration were increasingly hopeful about the latest Mideast diplomatic development.

Reagan's comment came in a brief exchange with reporters as he boarded his helicopter for a five-day California vacation. Several hours later the White House released a communique on Reagan's meetings Monday and Tuesday with Saudi Arabia's King Fadh, in which the president "renewed his pledge" to support his 1982 peace plan "in direct negotiations involving the parties most concerned."

"We're being optimistic about it," Reagan told reporters in reference to the Hussein-Arafat "framework for common action" that was concluded Monday in Amman.

A senior administration official who briefed reporters at Point Mugu, Calif., where Air Force One landed with the vacation-bound president, referred to the "framework" agreement as "a milestone" but also termed it "one step in a long road."

"Before, there had never been a Palestinian commitment to the peaceful resolution of the problem. Now there is," said the senior official, who did not permit use of his name.

The official avoided placing the acceptance directly within the "framework" of U.N. Security Council resolution 242, which the administration has singled out as an essential foundation for Arab-Israeli talks.

Diplomatic sources and press reports from the area said that the principle of trading territory for peace, which is the basic bargain envisioned in resolution 242, is endorsed in the "framework" agreement, but that the resolution is not mentioned by name.

The senior official briefing the White House press corps said the agreement as he understands it "implies the acceptance of the major principle of resolution 242."

State Department officials said it seemed significant that the Hussein-Arafat agreement was reached while the Saudi king was in Washington, in time for the Arab leader to discuss the accord with Reagan.

One reason for this might have been a desire of Hussein, Arafat and Egypt's President Hosni Mubarak to involve the Saudis as much as possible as backers and even sponsors of the agreement.

Fahd is principal author of the September 1982 Fez declaration of the Arab League, which is the most recent unified position of the Arab states on the conflict with Israel. The Hussein-Arafat framework goes beyond the Fez plan. For one thing, it does not call for an independent Palestinian state having Jerusalem as its capital.

In yesterday's U.S.-Saudi communique, Fahd spoke of the Fez plan as providing "a just basis for negotiations leading to a comprehensive peace."

Reagan in turn "expressed his appreciation for the Fez consensus, positive elements of which have been recognized by the United States."

The communique said Reagan and Fahd "stressed that a stable peace must provide security for all states in the area and for the exercise of the legitimate rights of the Palestinian people."

Regarding Lebanon, according to the communique, Reagan and Fahd "agreed on the need for rapid restoration of its sovereignty, independence and territorial integrity." They also pledged support for efforts to bring a speedy end to the Irani-Iraqi war.

The meetings of Reagan and Fahd, the communique said, "charted the course for continued development of U.S.-Saudi relations."