You really shouldn't hesitate to take a vacation simply because you don't have a companion to go along, but solo travelers do face certain problems that initially can seem daunting.

The big worry for many is loneliness. Dining by yourself, when you would rather have company, can be depressing even in Europe's most fascinating cities. And it can cost more to travel solo since there's no one sharing the price of hotel rooms, a cabin on a cruise ship or the rental car. Most escorted tours carry a "single supplement" charge, which may be 20 percent or more above the per-person price paid by a pair traveling together.

Some people thrive on traveling alone. They prefer going where they want, when they want. They will take their chances with lonesome evenings; and they will accept (reluctantly, as the price for independence) paying for a double room because the hotel has no singles, often the case in Europe.

But this is not everyone's idea of vacation fun.

If, instead, you are a solo traveler looking for company or who wants a good deal -- or both -- there are ways to combat the dilemmas of traveling alone. Go on an adventure: A little-recognized reward of an adventure holiday -- a week white-water rafting down the Colorado River, a 30-mile hike in the back country, overnight trail rides in the mountains -- is the camaraderie that emerges even in a diverse group with an age range spanning several generations. You may not find romance, but you won't be alone dining around a campfire.

And when your lodging every night is a tent, you don't have to pay a single supplement.

Sobek International of Angels Camp, Calif., one of the country's major adventure trip outfitters, organizes tenting expeditions throughout the world, from leisurely walks in Scotland to expert-class mountain climbs in the Himalayas. The firm estimates that 60 percent of its customers are singles. Most are in their mid-30s, but solos in their 70s have signed up, too. The single supplement for these trips applies only to occasional nights in a hotel or inn.

Trek America/Trek Europa, another adventure outfitter, features 14-person "maxiwagon" tours, with camping along the way, in the United States, Europe and North Africa. A 13-day, six-nation alpine excursion is $412 per person (tent, campground fees, van and leader), plus $50 for the food kitty. The trips, full of singles, are limited to ages 18 to 38. The itinerary is loose, so the group can linger when and where it chooses. Occasionally the group checks into a small hotel, but shares generally are easily arranged.

The Sierra Club, American Youth Hostels and a number of wilderness societies also offer group hiking, cycling, canoeing and sailing vacations almost anywhere in the world, including a good selection within a short drive from Washington.

For more information: Consult adventure travel guidebooks, available in large bookstores, and a travel agent. Also: Sobek, Angels Camp, Calif. 95222, (209) 736-4524; Trek America, Box 127, Staten Island, N.Y. 10309, (800) 221-0596.

* Take a cruise: "I personally believe that a cruise is the best vacation for singles," says Pam Zirkel, who heads the Cruise Company of Georgetown, a travel firm specializing in cruises. True, she just might be biased, but she's speaking from observations gained on more than 30 cruises, many of them as a solo traveler.

"There are so many opportunities to meet people," she says. As a woman, she feels easier talking to a stranger in the cruise ship lounge than she would, for example, in a Waikiki Beach hotel. Most cruise ships organize a singles party within hours of leaving port.

And most cruise lines sailing the Caribbean -- in an attempt to attract singles -- will arrange for you to book a shared cabin, if there's another solo willing. You pay one-half the double rate. Admittedly, it's a gamble that you will join someone compatible. But, "you're not in your cabin that much," says Zirkel, "so who cares?"

Carnival Cruise Lines offers quadruple cabins, which individuals can book on a shared basis. The full rate for a seven-day Caribbean cruise is a bargain $495. And with three other passengers in the cabin, you should find someone to talk to.

On many ships, a single booking a private room may have to pay from 50 to 100 percent more than the per-person cost of a double. But about 18 months ago, Princess Cruises -- the "Love Boat" line -- made many of its cabins available to singles at a 10 percent additional cost -- an "excellent" price, according to Zirkel. The line sails the Mexican coast, the Panama Canal, the Mediterranean Sea and the scenic Inside Passage to Alaska. A seven-day round-trip cruise from Vancouver, British Columbia, to Alaska's Glacier Bay ranges from $1,337 to about $2,000, plus 10 percent for single occupancy.

A tip: Younger singles generally are found on one-week cruises; the longer the cruise, the older the passenger list.

For more information: Consult a travel agent.

* Consider a guided tour in Europe: Renting a car for a single can be expensive, and it can isolate you. If you want contact with others, a tour provides companionship and the possibility of more.

Cosmos Tourama, one of the largest international tour operators, offers "guarantee shares" on all its European tours. In effect, you book half a double room. If Cosmos doesn't fill the other half, you don't pay anything extra.

Cosmos gears itself to the budget traveler, and more than one-third of its customers are singles or at least individuals traveling alone. The share arrangement seems to be accepted more by younger travelers, who "are not so set in their ways," says marketing vice president Jeffrey Joseph.

Cosmos also mixes English-speaking travelers from around the world, so the motorcoach isn't filled with Americans only.

Joseph says the tour escort matches roommates when the group forms at its first destination, and no match is necessarily permanent. On a vacation of his own, a decade ago, he shared with a 60-year-old man he describes as "totally obnoxious." It can happen, he acknowledges, but probably won't.

"Even with a roommate you don't like," he says, "on a tour you can spend time with whomever you want. You're not locked in to one person."

Cosmos' "Grand Alpine Tour," 16 days through the Lake Country of Italy and the Alps of Austria and Switzerland, is $541 to $556, depending on departure date. The price includes tourist-class hotels, 12 dinners, continental breakfasts daily and a Danube cruise. Air fare to Frankfurt, West Germany, is extra. Departures Saturday, through mid-October.

For more information: Cosmos Tourama, P.O. Box 482, Forest Hills, N.Y. 11375, (800) 22-0090. Or consult a travel agent.

* Try the Club Med: The organization has built 22 resorts around the world, and they are ideal for singles, who make up about 50 percent of Club Med's clientele. The rooms are double, but you pay only for your half on a share basis. There are lots of group activities; a party atmosphere; and dinner is at friendly tables for eight, formed as you walk into the dining room.

To introduce Club Med's new upscale island resort, Club Med Turkoise in the Turks & Caicos Islands, about 575 miles south of Miami, single rooms are available through Dec. 20. From New York, one all-inclusive week (including air fare) is $999.

For more information: Club Med, 3 E. 54th St., New York, N.Y. 10022, (212) 750-1670, or consult a travel agency.

* The Singleworld way: The annual "membership" fee is $18, which entitles you to join the cruises and tours designed for singles by Gramercy, a New York tour operator. The idea of the organization, now in its 28th year, is to help provide companionship for single travelers while offering them savings through shared hotel rooms and cruise ship cabins.

Spokeswoman Wendy Lowenstein is quick to point out that solo travelers are not social losers simply because they don't have a travel partner. The younger crowd may have friends who are unable to get away or can't afford a trip or prefer skiing to the beach. Older singles may be between romances, have only stay-at-home friends or have lost a spouse.

Some tours and cruise departures are limited to the under-35 age group; the rest are open to adults of all ages.

On a cruise, Singleworld's biggest seller, a tour escort helps arrange cabin matches and organizes an "ice-breaking" party the first evening at sea. The groups, ranging in size from 15 to 70 or more, dine together, and separate shore excursions are arranged.

Marriages have resulted from Singleworld trips, but more often travelers form friendships that are carried on both by letter and by repeat vacations together the following year.

A seven-day cruise on Norwegian Caribbean Lines' Skyward from Miami to the Mexican resorts of Cancu'n and Cozumel begins at $995, including air fare.

For more information: Gramercy's Singleworld, 444 Madison Ave., New York, N.Y. 10022. Or consult a travel agent.

* Find a travel partner: Like dating services, businesses exist to help you find a companion for trips.

When Jens Jurgen formed the New York-based Travel Companion Exchange three years ago, his biggest surprise was discovering how many clients, men and women alike, said they preferred a companion of the opposite sex. But not necessarily to share a room. Many, it seems, have an income that permits them to book private rooms, but they like the idea of having a friend down the hall.

Still, rather than traveling alone, they will go with someone of the same sex. But a great many, especially women, do request companions of the same sex only.

Jurgen has refined a questionnaire to aid in achieving companionable matches. Prospective travelers are asked to list such personal data as: marital status; age; smoking habits; occupation; extent of previous travel; travel preferences (tours/independent); travel budget (cut-rate/first-class); and, most recently, their attitude toward drugs.

The question of sex is raised discreetly: Shared accommodations or separate? A platonic relationship or something more intimate if it develops?

Even less worldly concerns can be important: Does the traveler board only with carry-on luggage? He or she will quickly lose sympathy for someone who is struggling daily with a pair of heavy suitcases.

Jurgen considers his service especially valuable for travel not available from tour operators, such as independent driving trips. His customers tend to be older travelers.

Jurgen charges $39 for a half-year membership. For that, you briefly describe yourself in his newsletter (no names) and search the list of other names for anyone who interests you. Contact Travel Companion Exchange for addresses, and then it's up to you to make the match.

Whomever you choose as a partner, you should do so as far in advance as possible, he says. And if the trip is to be an extensive one, now is not too soon to begin for 1986. A couple of dinners together or a weekend trip are ways to test the arrangement.

For more information: Travel Companion Exchange Inc., P.O. Box 833, Amityville, N.Y. 11701.

A final word: There is a certain art to finding the right trip to fit your mood. If you work in a busy atmosphere, with lots of people demanding your time throughout the day, a week or two alone on your own schedule may be well worth any single supplement.

On the other hand, if you sit sealed in a one-person office or shop, rarely seeing another human from 9 to 5, then you may prefer the festival atmosphere on a large cruise ship or the group activities of an escorted tour or adventure trip.