King Hussein's decision to increase Jordan's involvement in the Iranian-Iraqi war by sending volunteers to aid Iraq grows partly out of increasing concern about the impact of Iran's revolution on the stability of Persian Gulf states and partly out of a sense of obligation to Iraq's President Saddam Hussein.

Western diplomats and other analysts here, in reaching this assessment, also predicted that his decision will complicate his already tense relations with neighboring Syria and deepen divisions within the Arab world. At the same time, they added, it will not prove all that popular at home, particularly among Palestinians, who make up 60 percent of the kingdom's population.

Jordanian volunteers continued to sign up at recruitment centers here today, but in smaller numbers than yesterday. Ultimately, it is expected that several thousand, many either Army veterans or youths with basic military training, will join the Yarmouk Force.

The government is encouraging Jordanians to sign up by assuring all civil servants that they will continue to receive their regular pay and maintain their positions during their absence; one unconfirmed report said Jordan was also offering a high monthly salary to recruits.

The force is not expected to make much of a difference in the war, but the Jordanians are hoping it will provide a morale booster to the retreating Iraqi Army and prompt other Arab countries to follow Jordan's lead.

In seeking to understand why Hussein decided now to step up his involvement, Western diplomats note that the action came almost immediately after his tour of the Arab states of the Persian Gulf. This included a visit to the island sheikdom of Bahrain, where 60 Iranian-trained terrorists were arrested last month for allegedly plotting a coup and for other subversive activities there and elsewhere on the Arab side of the Persian Gulf.

"He is scared the Khomeini virus will spread," said one diplomat, referring to the Islamic revolution of Iran's Ayatollah Ruhollah Khomeini. "The Arab world is divided, lacking in ideology, self-confidence and goals, and the Khomeini revolution gives all this, plus an anti-Western drive."

Hussein is believed to have gained the backing of the gulf states because of their shared concern about a powerful, meddlesome Iran should it defeat Iraq and thereby provoke the fall of Saddam Hussein.

The Jordanian monarch has been by far the most vocal Arab supporter of Saddam Hussein and his war from the beginning, calling on the other Arab states to show more enthusiasm and support for what he and the Iraqi ruler regard as a pan-Arab struggle for legitimate Arab rights.

While the Arab states of the gulf have provided billions of dollars to Saddam Hussein to wage the war, Jordan has become Iraq's main transportation link to the outside world as well as serving as a kind of rear base.

The war, in fact, has brought Iraq and Jordan closer together than ever before, and Saddam Hussein has been showering loans and grants on the kingdom to improve the port of Aqaba, upgrade roads, build a new military and police college and buy $200 million worth of Soviet air defense missiles.

In return, Saddam Hussein has reportedly been urging the king to engage Jordan more directly on the Iraqi side and to stimulate greater material support from other Arab nations.

"The king does feel he has a personal moral debt to Saddam," said one Western diplomat. "Also, he really believes it is a holy Arab war."

Western diplomats, while not seeing any direct danger now to the Jordanian monarch, nonetheless feel he has made a decision that could easily aggravate his very tense relations with Syria, which views Jordan as an enemy and has taken Iran's side in the war.

Syria repeatedly has accused Jordan of backing the Moslem Brotherhood-led opposition to Syrian President Hafez Assad, and the two countries have come close to open confrontation several times in the past two years.

Furthermore, Assad is attempting to mobilize the Arab nations against Israel following the Israeli annexation of the Syrian Golan Heights, while King Hussein is calling on them to give top priority to the war against Iran instead. The effect has been to divide Arab loyalties and make Arab unity more difficult.

King Hussein's call for volunteers has received a mixed reception here.

Jordanian officialdom has hailed the decision in language similar to the speaker of the parliament, Bahjat Talhouni, who in a cable to the king yesterday called it "a noble and courageous stand" illustrating his "sincere Arab nationalism" in support of "usurped Arab rights."

But a sounding among some educated Palestinians here found most far from pleased. There was a feeling that the king's show of Arab nationalism was misdirected, particularly at a time when most Arab nations are fearful of another Israeli strike either into southern Lebanon or against Syria.

Obviously taking advantage of this general Arab fear about Israeli intentions to embarrass the king, Iran today offered to send Iraqi volunteers from among its prisoners of war to Syria to help it liberate the Golan Heights from Israel.