If there's an area of travel where discrimination rears its ugliest head, it's singles traveling. America's travel industry seems to suffer from the Noah Syndrome: everyone in pairs.

Traveling solo in a double-occupancy world is punishable in a lot of subtle and not-so-subtle ways.

It usually means paying an extra supplement in a hotel or vacation package. It means getting a table somewhere near the kitchen door. It means suffering the stigma that you're frantically searching for Mr. or Miss Right. Women travelers who sit at a bar alone are considered unladylike and immediately stamped as "available."

Dena Kaye, in her excellent book, "The Traveling Woman" (Bantam Books, $2.95, 384 pages), says alone doesn't necessarily mean lonely.

"To me, being alone is something I associate with choice. There are many times I am content to choose my own company.

"Heaven knows, there are times when I have been just plain lonely. It comes over me in a wave, especially when I see things that are wrenchingly beautiful, or emotional stirring. Loneliness and undefinable longings are quite natural."

Unfortunately, the penalty for traveling unattached can range from several dollars to several hundred. Hotel and resort rates are always skewed in favor of couples.

Of many possibile examples, the Detroit Plaza Hotel offers two persons a two-night, three-day plan for $99.50. A single person booking the same plan pays the same thing: $99.50.

At the Lake Buena Vista Hotel in Orlando, Fla., a three-night plan will cost two persons $244. A single pays $230.

An Eastern Air Lines hotel and car package for seven days in Orlando is priced at $583 for two persons. A single traveler pays the same thing.

People often travel alone by choice. There are advantages like independence, freedom in shaping activities, and the chance to meet people.

Maybe singles go unaccompanied because family or friends have different interests, vacation schedules, limited budgets or other plans. Maybe they're widowed, divorced -- even married -- and have rotten luck traveling with others. Maybe it's a business trip. Or they just need to break away for a little solitude.

Whatever the reason, single travel, like the single life style, is growing in acceptance. According to the 1980 National Travel Survey conducted by the U.S. Travel Data Center, 175 million trips, or 39 percent of all domestic trips, were taken by single persons. Singles accounted for 33 percent of all domestic vacationers.

Club Mediterranee, more than anyplace else, has wrapped a loving arm around the single traveler. Some 44 percent of its clients are single. It doesn't charge a supplement for singles, but all singles automatically get roommates -- of the same sex. Club Med (there are more than 80 clubs worldwide) pioneered the prepaid vacation package 30 years ago.

Some tour operators have guaranteed share plans, which means a roommate is guaranteed and there is no single supplement.

But the travel industry generally is still in the ice age when it comes to single travel, and the root cause is economics. Hotels figure that having two guests in one room means more food consumed, more liquor drunk, more laundry cleaned and more tips for everyone. If hotels do have single rooms, they are apt to be cramped and poorly located in the hotel.

The single traveler needn't despair; there are some solutions.

Probably the best way to beat the system is to join it. Ask the tour operator or travel agent if he or she knows of another single willing to make a tandem. It's risky, but you've got a 50-50 chance of it turning out just dandy. At the least you'll avoid the annoying single supplement.

Travel during the off-season. Some tour operators waive the single supplement on off-peak tours. They often don't broadcast it, so singles should contact a travel agent.

Try approaching cruise lines, where the single supplement is normally stiff. Some lines have a sort of standby service for singles when double cabins are unsold. You pay only the per-person charge on the double rate. Commodore Cruise Lines' Caribe has dozens of truly single cabins.

The fourth approach is joining a singles travel club. These are not dating, or so-called swinging, singles clubs, but they do match single travelers with compatible travel companions. Not many travel agencies specialize in single travel, but tenant associations, employe groups and such are mostly social clubs with occasional travel programs like ski weekends, New York theater weekends, etc. The clubs buy bulk space from travel agencies or tour operators or they charter buses.

Some single travelers create their own dilemmas. "Single people have got to go into travel looking to broaden their horizons and not worry about who they're going to meet," says one travel agent. He believes people are programmed to twosome travel and don't consider the plusses of traveling with a peer group, where there's no arm-twisting to pair off.

Most of the specialists in single travel are tour agencies on either coast that work to pair singles with singles to avoid the single supplement.

New York-based Singleworld ran its first singles tour in 1957. It offers some packages for those under 35 and others for vacationers of all ages. For a $15 membership fee, anyone single or traveling alone receives newsletters announcing special events, trips, discounts and travel information keyed to singles.

Singleworld is the largest broker of packaged tours for single travelers. "The time has come for single travel," said Natalie Strauss, a reservationist with Singleworld. "There is a big professional market; a lot of singles with the money to travel. Our phones are ringing constantly. We arrange shares (roommates) of the same sex, smoking preference, that kind of thing."

Another single specialist based in New York is Travel Mates, which runs programs for under-35, up-to-50 and over-50 age groups, and the Widows Club, which claims 5,000 members (20 percent of whom aren't widows).

Grand Circle Travel, based in New York, specializes in tours for older people. Grand Circle claims the fastest-growing travel segment in the country is the older American, age 50 and up. Because many are retired or widowed and traveling alone, Grand Circle will pair them with travelers of similar background on tours ranging in price from $750 to $3,000-$4,000 for a global trip. (A free booklet, Tips for the Mature Traveler, is offered by Grand Circle, 555 Madison Ave., New York, N.Y. 10022.)

Here are some rules to follow for the solo traveler:

Relax. You're not the first solo. Lots of people travel along, prefer it, and enjoy advantages like shopping when they want to go shopping and not being dragged to some drafty museum or forced to photograph sunrises.

Don't take any guff. Saying "One, please" to the maitre d' shouldn't be a cue to shunt you to the back of the line while tables for four sit vacant. If the headwaiter wants to seat you near the potted palm, tell him to sit on it -- and seat you elsewhere.

Face it, there will be lonely moments, so bring that book or needlepoint you've been wanting to finish. A camera can be a good companion, or you can spill your thoughts into a diary or letters to friends.

Pamper yourself. Breakfast in bed, flowers, an expensive bottle of wine can help chase your sadness.

If you're shopping for a packaged tour or cruise, pick one patterned after a favorite interest: photography, bridge, etc.

Companies specializing in single travel include the following (your travel agent can supply more information): Singleworld Tours, 444 Madison Ave., New York, N.Y. 10022; Travel Mates, 574 Fifth Ave., New York, N.Y. 10022; The Widows Travel Club, 17 E. 45th St., New York, N.Y. 10017; Travel Match, P.O. Box 22, Lenox Hill Station, New York, N.Y. 10021, and Singles Travelworld, 11660 Chenault St., No. 119, Los Angeles, Calif. 90049.