Secretary of State George P. Shultz reassured Israel yesterday that the United States will continue to avoid dealing with the Palestine Liberation Organization. In what appeared to be an implied warning to the PLO, Shultz said that "those who perpetrate violence deal themselves out of the Mideast peace process."

Shultz's comments, after a meeting with Israeli Finance Minister Yitzhak Modai, were an attempt to ease Israeli concern that the administration might authorize Assistant Secretary of State Richard W. Murphy to meet with a Jordanian-Palestinian delegation that would include Nabil Shaath, an adviser to PLO Chairman Yasser Arafat.

Referring to reports that President Reagan plans a major new arms sale to Jordan, Shultz said "it is clear to us that Jordan has definite security problems" and added that "help from the United States is justified."

He insisted, however, that Reagan "has made no final decision about exactly what he might propose or when he might propose it."

Shultz and Modai appeared briefly before reporters to announce that the United States, recognizing Israel's economic retrenchment, is releasing the first $750 million of $1.5 billion in special economic aid approved last month by Congress for Israel.

However, they were besieged by questions about possible U.S. moves for new peace talks between Jordan and Israel.

The questioning was so intense that Shultz, recalling his service as treasury secretary in the Nixon administration, remarked to Modai that "it used to be that I thought economics was important," yet the fact that the United States was turning over to Israel three-quarters of a billion dollars "doesn't even get a question from the press."

"It's a new day," he added wryly.

U.S. and diplomatic sources said Thursday that the administration is considering sending Murphy, assistant secretary for Mideast affairs, back to the region to meet with a delegation chosen by Arafat and King Hussein of Jordan.

Shaath's inclusion among the proposed Palestinian members roused Israeli concern that the United States might be abandoning its 10-year policy of refusing to deal with the PLO unless it accepts Israel's right to exist.

U.S. officials deny that any policy change is contemplated. However, they also have said that, since defining precisely what constitutes PLO membership is difficult, it might be contended that Shaath does not belong officially to the umbrella organization of Palestinian groups.

Shultz sidestepped questions yesterday about how the United States would decide whether proposed delegates are PLO members. Instead, the Cabinet member sought to play down the idea that the United States is planning some major policy shift or dramatic move in the Middle East, saying:

"Sometimes I read in the rumor mill of what we're thinking, and I say somebody is insulting us. They must think we have lost our marbles if they think we are considering this, that or the other thing."

Referring specifically to the PLO, he said, "Our conditions for talking with the PLO remain as they have been for many years."

He immediately added: "I would have to say that the upsurge of violence recently certainly presents a problem . . . . I think it is very clear to us that those who perpetrate violence deal themselves out of the peace process."

He did not elaborate. But U.S. officials suggested privately that the remark was intended as a bow to Israeli charges that the increased PLO presence in Jordan is linked to a recent surge of murders and other terrorist acts inside Israel.

The official U.S. response to these charges has been that Hussein is opposed to terrorism and that, while he has permitted the PLO to strengthen its administrative presence in Amman, the Jordanian capital, he has not permitted terrorist groups to operate from Jordanian territory.

However, the officials suggested that Shultz's comment could be interpreted as a warning that, if the PLO hopes to win a role in the peace process, it must cease terrorism from any source and be more cooperative in fostering negotiations.

State Department spokesman Bernard Kalb, asked whether Shultz's remarks were aimed at the PLO and its possible participation in peace talks, replied: "I would simply say in the most general terms, if the shoe fits, wear it. But I'm not ruling in or ruling out."

In addition to the money for Israel, the State Department announced that it is drawing on appropriated supplemental funds to provide a $250 million cash transfer to Egypt and $53 million to Jordan to subsidize commodity imports and school construction.

The department said another $3 million will be allocated shortly for projects to aid Palestinians in the Israeli-occupied West Bank and Gaza Strip.

Modai, reiterating his country's refusal to deal with the PLO, said he is "positive that whatever our American friends are discussing with King Hussein and some Palestinian representatives are in line with this basic approach that terrorists are excluded from any discussions . . . . "

He also reemphasized Israel's strong opposition to U.S. arms sales to Jordan or Saudi Arabia.