Short Sailings Making a Big Impact : Moderately priced three- to four-day cruises seem to better fit today’s lifestyles.

Mini-cruises--those three- and four-day weekend and midweek getaways--are the hottest vacations going. In 1991, some 1,487,000 passengers set out on two- to five-day-long cruises, according to CLIA (Cruise Lines International Assn.).

Short cruises seem to fit the new lifestyles of the ‘90s. People are opting for several small vacations during the year rather than one big one. Stressed-out individuals like the hassle-free environment of a cruise ship, where there’s no packing and unpacking, no worry about getting from point A to point B, or deciding where to eat dinner.

The newest wrinkle is family reunions aboard mini-cruises, so nobody has to host, cook or clean. For every 15 or so people, there’s usually a free or discounted escort or organizer’s ticket.

Short-cruise prices, already relatively moderate, can be reduced further when passengers opt for a cruise-only fare--one that eliminates the round-trip air fare, useful when a the traveler lives within driving distance of the port or wants to use frequent-flier miles to purchase his or her own plane ticket.

From Los Angeles, two cruise ships make year-round mini-cruises to Ensenada in Baja California, calling as well at Catalina Island and, on four-day midweek sailings, San Diego. Both sail on Friday afternoons and return Monday mornings on the weekend cruises, then sail Monday afternoons and return Friday mornings on the midweek sailings.

But Royal Caribbean Cruise Line’s 1,512-passenger Viking Serenade and Norwegian Cruise Line’s 752-passenger Southward are so different from each other that they offer a clear-cut choice of cruise styles.

The Southward is an older, smaller, more intimate vessel with the additional attraction of costumed Universal Studios characters often on board. Characters ranging from Groucho Marx and Frankenstein to Woody Woodpecker and Marilyn Monroe may show up on deck and pose for photographs. The line says its mini-cruises primarily draw passengers between the ages of 25 and 44.

Cruise-only fares on the Southward start as low as $375 per person, double occupancy, for three-day cruises, $395 for four-day cruises, during economy season--from Oct. 16 through Dec. 18 on three-day cruises, now through Dec. 14 on four-day cruises. But these prices apply to only seven cabins on the ship; after they’re booked, expect to pay from $420 to $1,045 per person, double, for other accommodations. Children sharing the room with two full-fare adults pay $195-$250 without air fare. With air fare included, the full-fare range goes from $525 to $1,195 per person, double.

The Viking Serenade is much bigger than the Southward, and with its recent refurbishing, a more glamorous-looking ship. When the remodeling was done last year, a former car-ferry deck was converted into two decks of brand-new cabins, including 10 of the very lowest-priced, bottom-category cabins. These inside, windowless cabins contain two lower beds, color TV sets and modern bathroom units with showers and pastel fixtures. At value season--between Nov. 27 and Dec. 18--they go for as little as $345 per person, double, for a three-day cruise without air fare.

The lowest-priced outside cabins were also added last year, and have portholes instead of windows; three-day fares here are $645 per person, double occupancy, for economy season, slightly higher the rest of the year, without air fare. Two kids sharing the same room with their parents travel for $200-$260 apiece without air fare. Full-fares with air fare range from $495 to $1,845 per person, double.

The two most glamorous ships in the short-cruise market sail from Miami: the jazzy, neon-bright 2,050-passenger Fantasy from Carnival Cruise Line, and the polished, 1,600-passenger Nordic Empress from Royal Caribbean Cruise Line. But with round-trip air fare included from major U.S. gateways and the option of a reasonably priced pre- or post-cruise add-on to Orlando, the Florida Keys or South Florida golf resorts and spas, the cruise could be tied into an appealing weeklong package for travelers from all over the United States.

Again, the personalities of the two ships could not be more different: The Fantasy is a wired, boogie-all-night ship with jaw-dropping decor, including 15 miles of neon tubing strung out around the public rooms so that they gradually change color like a juke box, while the Nordic Empress is a romantic, pretty-in-pastels vessel. Both call in Nassau and, on four-day cruises, Freeport as well. The big itinerary choice is between Fantasy’s day at sea with the casino, shops and lounges going full blast, or Nordic Empress’ day on CocoCay, a private island beach with water sports and a barbecue.

Prices range from $459 to $1,339 per person, double, on the Fantasy, including round-trip air fare, and from $515 to $1,635 per person, double, on the Nordic Empress with air fare. Fares vary depending on the length of the cruise, the season and the quality of accommodations, but bear in mind that except for suites, all the cabins on each ship are virtually the same size since they are built on a modular basis.

A third brand-new ship, the 1,056-passenger Royal Majesty from Majesty Cruise Line, a new upscale offshoot of Dolphin Cruise Line, made its inaugural voyage from Miami on Sept. 18. The three-day cruise calls at Nassau with a daylong jaunt over to Royal Isle for beach and water sports, while the four-day itinerary adds a day in Key West as well. (One of the attractions of Royal Majesty is its smoke-free policy. Both the ship’s dining room and 132 of its staterooms have been designated nonsmoking, a first in the cruise industry.)

Prices on these short cruises range from $489 to $1,539 per person, double, including round-trip air fare from 96 gateway cities. West Coast cities have a $95 add-on that includes overnight hotel accommodations before sailing.