RIYADH, SAUDI ARABIA, DEC. 12 -- Saudi Arabia's religious police, who enforce prohibitions against alcohol, unveiled women and mixing of the sexes, have become increasingly aggressive in their patrols, even entering private homes to arrest Saudis and foreigners violating these bans.

The stepped-up activity of these police -- known in Arabic as mutawein, or volunteers -- is due partly to religious conservatives' fears that this country's adherence to a strict form of Islam may be diluted by the presence of U.S. and other foreign military forces, many Saudis and diplomats said.

"There is a kind of worry about foreign influence in this country," one diplomat said, "and it came to a head when some foreign forces arrived."

The newly aggressive behavior of the mutawein, who brandished guns at startled party-goers and jailed foreigners and Saudis in two recent incidents, has angered and worried many Saudis who favor a more open, tolerant society here, and has added to the tension in a country already facing the possibility of a war.

In a celebrated case two weeks ago, the mutawein raided a party at the home of a prominent businessman in Jiddah, arresting male and female guests for allegedly drinking alcoholic beverages and mixing with members of the opposite sex to whom they were not related. Among those arrested was a member of King Fahd's staff, several sources said.

At least two businessmen at the party were convicted the next day and given two-year jail sentences, and the member of Fahd's staff received a 10-month sentence, several sources reported. The 14 women taken from the party and jailed were citizens of other Arab countries, he said.

The Jiddah incident followed a raid in Riyadh last month in which the mutawein, armed with guns, sticks and axes, stormed a party in the home of a French citizen. They reportedly broke furniture and assaulted some of the guests, tearing their clothes and pointing guns.

Forty-six Westerners, including three Americans, who were not affiliated with the U.S. government, were taken to a mutawein detention center where they spent several hours before being rescued by their embassies, sources said.

The U.S. Embassy and several other Western missions here protested to the Saudi government over the violence used in the incident, sources said.

Charges against the foreigners of using alcohol were dropped and neither of the raids was reported in the local, state-guided media. While the government reportedly has sought to quietly contain the more zealous of the mutawein, it clearly does not want a major confrontation with the religious establishment at this time.

The mutawein also have become more zealous in monitoring women, many Saudis have reported. Filipino nannies picking up children at schools have been harassed for not covering their hair; cars have been stopped because mutawein spotted women they regarded as inappropriately covered, and Saudi men have been challenged to prove women accompanying them are relatives.

These incidents have worried many Saudis and foreigners for several reasons. Although the mutawein can detain anyone found with alcohol or in mixed company, they normally do not enter homes, whose privacy has long been sacrosanct in Islamic tradition. In addition, the mutawein, who are supposed to patrol with the regular police, do not normally carry weapons.

Many Saudi women resent the mutawein's harassment, which they say reflects a misplaced preoccupation with unimportant details when their country is facing more important challenges.

A Saudi woman told of an American friend, whose brother is among the U.S. troops stationed in Saudi Arabia, who was recently chided by mutawein while shopping for showing her hair, although she was wearing the long robe traditionally worn by women here. She shouted at the men to "go away and leave her alone since her brother is helping protect Saudi Arabia," her Saudi friend reported.

As their name suggests, the "volunteers" can be self-appointed, but most of the mutawein receive a stipend for their patrols from the powerful religious authorities. They usually have long, untrimmed beards and wear the traditional male Saudi robe shorter than other men do because they believe this is how the prophet Muhammad dressed.

The Jiddah incident, in particular, has spread alarm among many Saudis, because the Red Sea port has traditionally been Saudi Arabia's most relaxed and tolerant city. It also is home for many of the country's wealthy business and merchant families.

The raid "was a very big event because it involved some famous businessmen. All of {Jiddah} is talking about it," one resident said. Although the gathering was illegal under Islamic law, "we will not accept that way of handling matters," he added.

The incident "has created a lot of unrest, especially among the businessmen because, until now, they were allowed to do at home what they wanted to do," a diplomat said.

Several embassies have complained to the government about the mutawein's activities, he added, because with tension already running high in Saudi Arabia, there is no need to "create panic among the foreign community."

He attributed the mutawein's new profile in Jiddah to the recent transfer of many of them out of Saudi Arabia's Eastern Province in order to avoid clashes with U.S. soldiers streaming into that area. Apparently, he said, many of the mutawein moved into Jiddah where they have "no familiarity with local customs."