Orbitours, an Australian company, offers trips to Vietnam, Laos and Cambodia that originate in Bangkok. A four-day, three-night Vietnam package costs about $400 plus air fare. For a brochure, write Orbitours, Seventh Floor, Dymocks Building, 428 George St., Sydney, N.S.W., Australia, or phone (from the United States) 011-61-2-221-7322.
Another popular tour arranger is Diethelm Travel, 140/1 Wireless Road, Kian Gwan II Building, Bangkok 10500, Thailand; phone 011-662-255-9150.
Adventures in Paradise, also in Bangkok, has a representative in New York at 155 W. 68th St., Suite 525, New York 10023, phone 212-595-5782.
A Canadian company that handles Vietnam tours is New Asia Tours, 1063 boul. St.-Laurent, Montreal, Quebec H2Z 1J6; phone 514-874-0266.
These operators make all arrangements out of Bangkok, including transportation, accommodations and sightseeing. Start making your plans at least a month in advance.
Travel literature on Vietnam is limited, but two guidebooks that have short
sections on the country are The East Asia Handbook (International Publishing Group) and Southeast Asia on a Shoestring (Lonely Planet Publications).
I'm planning a trip to Sweden and would like to rent a place for a couple of weeks. Do you know of any agencies that rent apartments by the week there? K.R., Philadelphia
The local tourist offices in Sweden - there are 685 - can help visitors find temporary apartment space or a guest room in a home, according to a spokesman for the Swedish Tourist Board.
If you write or call the board and ask for a listing of tourist offices, it will send you addresses for the 14 regional offices as well as those for the larger cities.
Also ask for the Sweden folder, which describes events in the cities and the transportation system, and has tips on cutting costs through visitor- discount programs.
Contact the Swedish Tourist Board, 655 Third Ave., 18th Floor, New York, N.Y. 10017; phone 212-949-2333.
I am interested in spending time at a health spa on the East Coast. Can you recommend some low-cost spas? L.B., Philadelphia
The good news is that the spa market is booming, and so is the number of books and services that can help you find one. The bad news is that "low-cost spa" is, in many cases, a contradiction in terms.
At a typical full-service spa, you can expect to pay at least $200 per day, per person, and quite likely more. You can keep costs down by going during the off-season and, where possible, using a resort whose program has optional features.
A spa with a simple exercise option, for instance, would be less costly than one where every facet of your day is programmed. Signing up for four days would help keep costs down, too, over a full-week package.
Here are some companies that arrange spa holidays:
* Spa-Finders, 784 Broadway, New York, N.Y. 10003; phone 800-255-7727, has a worldwide catalogue for $4.95 plus $2 shipping.
* Health Travel International, 222 Wisconsin Ave., Suite 6, Lake Forest, Ill. 60045; phone 312-234-5652.
* Sante International, 55 Park Ave., Suite 1NW, New York, N.Y. 10016; phone 212-779-8333.
The following spa guides are recent, but you can expect that the prices they mention have changed somewhat:
* Fodor's Health & Fitness Vacations by Bernard Burt, (Fodor's Travel Publications, 1989), $13.95.
* Select Spas by Anne Harding (McGraw-Hill, 1989), $12.95.
* The Spa Book by Judith Brode Hirsch (Perigee Books, 1988), $10.95.
* The Best Spas by Theodore B. Van Itallie and Leila Hadley (Harper & Row, 1988), $21.95.
We read about a clothing-optional Caribbean resort called Club Orient on St. Martin. Where can we get information on it and similar resorts? J.S., Bryn
Club Orient's address is simply 97150 St. Martin, French West Indies.
Promenade Travel in Bloomingburg, N.Y., books trips to Club Orient, as well as to other clothing-optional resorts. It offers a 28-page booklet of destinations, including the Caribbean, for $10. For the booklet or for more information, call 800-828-9356.
A company called Caribbean Travel Naturally also books guests into a number of Caribbean resorts where clothing is optional. Its number is 800-476-6833.
Donald D. Groff welcomes questions from readers and will reply to each. He will answer those of general interest in this column. Write Donald D. Groff, Travel Department, The Inquirer, Box 8263, Philadelphia 19101.