Staying on the Safe Side; Geneva

Street crime is so rare in Geneva, the cosmopolitan Swiss city that houses the European headquarters of the United Nations, that an occasional purse-snatching will be reported in the ''Faits Divers'' columns of the local newspapers.

Residents warn foreign visitors to stay away at night from the Les Paquis district. This neighborhood, behind the Quai Wilson on the west bank of the lake, is studded with taverns, some sleazy, and nightclubs, but is also home to quite a few of the most genuine Genevois, and during daytime is worth a stroll to savor its populist atmosphere.

Car thefts in general have lately become a plague in Geneva and car-rental companies warn customers to be careful. Although separate figures for auto thefts were not available, authorities said that 36,016 crimes were reported in 1989, a rise of about 3,000 over 1988.

The criminal specialty of opulent Geneva is victimization of affluent guests by international and local adventurers. Diplomatic conferences and other gatherings that bring well-heeled visitors to the city also attract high-class prostitutes and confidence swindlers from all over Europe; they look for easy marks in hotel lobbies and night spots.

The police department of the Canton of Geneva seems to know fairly well what is going on, although its force is little apparent. However, not every foreign delegate who has been rolled by a new-found friend will report the experience to the authorities.

If you take a night train to France, Spain or Italy from Geneva's Cornavin railroad terminal, watch out for travelers without luggage who may walk from coach to coach as if looking for someone. They may indeed be searching out a prospective target. Thefts on night trains in Southern Europe are no rarity; victims are often rendered defenseless by knockout sprays. Sleeper attendants warn passengers to double-lock their compartments, but robbers sometimes force locks and snip chains. Most attendants in sleeping cars no longer watch their cars throughout the night, as they once did, but go to sleep around midnight.