The Reagan administration came under intensified and competing pressures yesterday from Israel and Jordan regarding the volatile situation in the strategic Persian Gulf.

Israeli Defense Minister Ariel Sharon and Jordan's Crown Prince Hassan, in separate meetings with senior administration officials, expressed grave concern about the potential impact of developments in the 20-month war between Iran and Iraq. But their viewpoints were very different.

Sharon, following a lengthy meeting with Defense Secretary Caspar W. Weinberger, expressed public concern that the United States might back a new Arab "coalition" based on Iraq, which he described as "one of the most radical countries of the region."

The coalition, according to Sharon, could include Saudi Arabia and Jordan "with the participation or support of Egypt."

Such a coalition, Sharon said, would be a "threat to peace," and he left no doubt that Israel would strongly oppose it.

Israel is widely reported to have given secret military assistance to Iran in the Persian Gulf war because it considers Iraq a greater menace.

On the other hand, Hassan viewed Iran as the greater menace, saying its victories against Iraq could spill over to "jeopardize the entire resource-rich region."

Speaking to reporters after meeting Secretary of State Alexander M. Haig Jr., he called for greater U.S. diplomatic activity to "check the limits of the conflict" and contain the spread of the Iranian revolution.

The United States has taken an essentially neutral position in the Iran-Iraq war, which broke out with an Iraqi invasion while U.S. hostages were being held in Tehran.

Washington has said and done little about the conflict since then, but recently it has come under renewed presssure to become involved as a wave of worry about an Iranian victory has engulfed conservative Arab states.

Haig is expected to address the Persian Gulf war and other Mideast issues in an address tonight at the Chicago Council on Foreign Relations.

The conflicting perspectives and cross-purposes of Jordan and Israel spilled over to the Washington arena in other ways as well.

Hassan, younger brother of King Hussein, said there is a "a great danger" of Jordan being overwhelmed by threats and challenges.

At a luncheon appearance at the Middle East Institute, he said Israel has a qualitative military edge over the entire Arab world and called for "a fairhanded approach" by the United States to strengthen Jordan.

Weinberger, in a trip to the area in February, discussed possible sales of sophisticated U.S. arms to Jordan. This touched off an immediate storm of protest in Israel, and Israeli authorities recently renewed the protest.

Sharon, after his Pentagon meeting yesterday, said, "I emphasized the danger of arms sales to Jordan as a threat to peace."

With Israeli encouragement, large numbers of U.S. lawmakers have mounted a campaign against major new U.S. arms sales to Jordan.

At least 45 senators were reported yesterday to be co-sponsoring a resolution against proceeding with sale of F5G fighter planes, Stinger antiaircraft missiles or other sophisticated gear under consideration for that country.

In yesterday's meeting with Sharon, Weinberger agreed to visit Israel in August or September, according to a U.S. briefing for reporters.

Despite some expectations to the contrary, officials said there is no plan to restore the suspended U.S.-Israeli strategic cooperation agreement during Sharon's current visit.

Nonetheless, Weinberger and Sharon agreed on new steps of military cooperation, involving consultations by small teams, while the largely symbolic strategic agreement remains in abeyance.