In the wake of renewed terrorist infiltration across the Jordanian border, Israel today expressed growing alarm over political unrest in Amman resulting from King Hussein's rapprochement with the Palestine Liberation Organization and the Arab rejectionist states.

Shortly after four Palestinian terrorists were killed by an Israeli Army patrol about one-half mile inside Israel this morning, the army said in a communique that it "takes a serious view" that Jordan, which has been quiet for several years, "has begun to serve as an active sector for the terrorists."

Moreover, a high-ranking Israeli officer, Gen. Avigdor Ben-Gal, commander of the northern region, issued an oblique warning that if further attacks are found to involve Jordanian complicity, Jordan will not be immune to retaliatory attacks by Israel.

Ben-Gal, in a radio interview, sugguested that recent terrorist forays across the Jordan River may be linked to Hussein's attempt to mend divisions with militant Arab factions that go back to the 1970 "Black September" purge of the PLO and the expulsion of Palestinians from Jordan.

Today's terrorist attack, the second across the Jordan River in six weeks, occurred near dawn near the Tirat Zvi Kibbutz, just south of Belt Shean in the upper Jordan Valley below the Sea of Galilee.

Israeli defense officials said a routine patrol spotted a hole in a border fence and footprints along a dirt roadway that is swept twice daily to pick up traces of infiltrators.

Authorities said 20 minutes later a search force engaged the terrorist squad in small arms fire, killing all four members. The Army said the terrorist were wearing camouflaged uniforms over civilian clothes and, according to papers they carried, had traveled from Syria-through Jordan-to reach the frontier.

Officials said they belonged to Fatah, the largest group within the PLO, and were carrying hand grenades and rifles. The officials said the terrorists also carried leaflets written in Arabic and a Fatah flag.

A similar attempt to infiltrate across the Jordan about 20 miles north of Jericho was surprised by an Army patrol on March 10, and four suspected terrorists were killed.

For the last several yars, attacks across the Jordan had been relatively infrequent, with the last one occurring in August 1978.

Ben-Gal sai that if the attacks are connected to Hussein's hardening stance alongside the rejectionist states and his rapprochement with the PLO, Israel will take "certain political steps." If the attacks continue and appear to be sanctioned by Jordan, Ben-Gal said, then Jordan will not be "absolved" from the possibility of retaliatory strikes, just as Lebanon has not.

For months, Israel has been routinely launching air strikes against Arab guerrilla training bases in southern Lebanon in retaliation for bombings and other terrorists attacks on Israeli targets.

An Army spokesman said today the military has no proof that the most recent attack was made in collaboration with the Jordanian Army.

But, he said, "on the other hand, six weeks ago we felt, well, it can happen now and then, and we won't say anything. Now, we have to say a word to warn the Jordanians that if this crossing had been successful and if we had to hit back, then maybe we would hit back on Jordanian soil."

Civilian officials were reluctant to issue public warnings, but one government source said, "We're very worried over what happened. We hope this does not mean there is a new arrangement to return to the pre-1970 free hand to the PLO to strike at Israel through Jordan."

Reports reaching Israel from Amman talk of growing political instabilility and rivalry between Hussein and his brother, Crown Prince Hassan, who is said to be adamantly opposed to the king's policy of rapprochement with the PLO and rejectionist states.

The Phalangist radio in Beirut has been reporting that an aircraft engineer was arrested over the weekend on charges that he had planted a bomb on a plane that King Hussein was to take to Vienna, but that the bomb was found before takeoff.

Two of the crown prince's supporters, Sharif Nasser Jemil, who is Hussein's uncle, and Razi Arabiat, head of state internal security are rumored to have died under mysterious circumstances in the past several days. Both men were said to have backed Hassan's opposition to any softening of Jordan's policy toward the PLO.

Haaretz, the Hebrew newspaper, quoted visitors from Amman as saying that Jemil died in an automobile accident, but that Hassan supporters believe the car was sabotaged. Arabiat was also said to have died accidentally, but details were not available.

Israeli sources said that Prince Hassan for years has been more anti-PLO than his brother, but they had no explanation for King Hussein's statements of outright support for the terrorist organization.

"What makes him [Hussein] such a champion of the PLO line, we don't know.Everbody counted Hussein among the moderates. Now something has happened there, and we don't know what it is," said one Israeli official.

Hussein also has caused some alarm here with his recent statements urging Soviet Union participation in the Middle East peace process.

In an interview in the Beirut weekly, Al Hawadess, Hussein complained that the United States had lost its position as a neutral arbitrator and added that "there must now be new international activity in which the Soviet Union and other parties concerned in the region could participate."