Some westerners here, long sheltered and favored by Libyan leader Muammar Qaddafi, were ordered tonight to begin immediately moving into evacuated Army camps that could be the targets of U.S. military action, according to European business managers.

It was not clear how extensive the moving orders were or to how many groups they apply, but they came less than 24 hours after an announcement by Qaddafi that such relocations were to be undertaken. No Americans working here were available for comment tonight.

In another development, diplomatic and church sources today revealed the disappearance and apparent arrest on Thursday of the Italian Catholic Bishop of Libya, together with three priests and a nun in the town of Benghazi, about 400 miles east of Tripoli.

[In Rome, the incident was confirmed Sunday by the Italian Foreign Ministry and church sources, United Press International reported. The sources said the five were seized by revolutionary guards, youthful militiamen loyal to Qaddafi.]

Earlier in the day, diplomats had tended to dismiss as rhetoric Qaddafi's statement that foreigners would be moved. But tonight, they were working late at their embassies and either refused to comment on any aspect of the situation or professed ignorance of it.

European managers told reporters privately tonight that they had been summoned by revolutionary committee members, the zealous vanguards of Qaddafi's revolutionary regime, and told to begin moving their employes immediately.

One Scandinavian businessman, who asked not to be identified by name when he talked to a reporter immediately after meeting with the revolutionary committee members, said, "We don't know what we're going to do, but we're stalling for time."

Qaddafi said yesterday that there are about 15 military bases already evacuated by the armed forces. The businessman here confirmed that the nominal reason for the move was to do "maintenance work" on the bases.

[Syria and Iran pledged Sunday to back Libya in its confrontation with the United States, Deutsche Presse-Agentur reported. A Syrian spokesman was quoted as saying the United States "has to realize it will not be the winner as a result of this aggression, but rather the greatest loser."]

According to church sources, Bishop Giovanni Martinelli, 42, and the others -- monks from the Philippines, Malta and Poland and an Italian nun -- were taken from the Franciscan Order's convent and residence in Benghazi, where they were sleeping, at about 11 p.m. on Thursday.

Their absence, a priest here said this afternoon, was not noticed until worshipers came for mass on Friday and found no one to conduct the service. Their rooms apparently had been ransacked at the time they were taken, this priest said.

There are about 100,000 Catholics in the country, most of them expatriates, including Filipino laborers.

There has been no official acknowledgment by the government of the detention and no hint of the motive, but the priest here said Libyan authorities have told church officials that the five members of the clergy are being held in a villa near Benghazi and treated well.

Initially, church officials were told the group would be released on Saturday, but they remained in custody tonight.

One Middle Eastern diplomat who closely follows developments in Libya's internal politics said tonight that he believed detention of the bishop may be part of a power play at this delicate moment by the revolutionary committees and guards.

About 1,000 Americans are still here, by most estimates, despite an order by President Reagan, first issued in 1981 and strongly repeated in January, that they should leave. About 8,000 Italians are in the country, together with 5,000 British citizens and about 2,500 West Germans and French.

Most were attracted by the high pay offered for their services in the oil industry and Qaddafi's various development schemes. Living in comfortable compounds, they have been well treated throughout the crisis of the last few months, and many said that they had nothing to fear from Qaddafi's government.

The Libyan leader has said repeatedly that he would not harm any Americans working here.

Qaddafi's philosophy of government, blending anarchist rhetoric and police state tactics, encourages zealots in the revolutionary committees and groups of revolutionary guards to take justice and sometimes policy into their own hands. In 1984, student committee members hanged several of their classmates in front of the student body on the university campuses here and in Benghazi.

The frictions between the guards and the regular Army often have been high. The murder in November of Hassan Ishkal, a senior Army officer close to Qaddafi, was believed by several diplomats to be a crucial moment in the showdown.

According to the Middle Eastern envoy's analysis, the revolutionary guards were seen as overplaying their hands by murdering a figure so close to Libya's leader, and a member of his own tribe. As a result, their power began to wane.

Now, as Libya faces the possibility of a serious military confrontation with the United States, the Army's professionalism and expertise is more needed than ever and its power, as a result, is perceived as increasing.

The detention of the priests and the role the committees are taking in pushing foreign employes to the military bases may be an attempt to reassert their authority, according to this reading of the situation.

It comes as the United States and Libya are locked in a diplomatic struggle following in the aftermath of their military confrontation in the Gulf of Sidra, the bombing of a TWA airliner and the bombing of a Berlin discotheque frequented by U.S. soldiers, which the United States has blamed on Libya.