WHENEVER zoologist Margaret Collins of Howard University departs for her research outpost in the rain forest of Guyana, she's apt to take along a group of vacationing amateurs who have paid their own way to help her study the habits of termites and other crawly things.

Deep in the interior of this tiny South American nation, Collins' charges will be participating in an unusual vacation experience that is becoming something of a trend. Instead of a typical holiday, they will be volunteering their outdoor labor to science for two weeks in conditions little better than primitive.

The union of student and scholar is a happy one: It links a certain breed of traveler seeking more meaning from a trip than normally found in the casual tourist whirl with the scientific research community, which--in the face of funding cutbacks--welcomes the traveler's money and hours of labor to support its studies.

As a contribution of funds and service to further research, trip costs under certain circumstances can be deducted from taxes as a charitable gift.

In recent years, three organizations have begun matching up researchers and volunteers for two- and three-week projects in the United States and abroad:

* Earthwatch: This year the Belmont, Mass., group is sponsoring 80 university and museum programs around the world, including Collins' ongoing study of rain forest fauna on the Mazaruni River. One of the most popular trips involves attempts to teach language to dolphins in Hawaii ($1,495). Other summer and fall projects: Plants of the Rockies (Colorado, $825); Romania's Caves ($1,175); Early Man in Africa (Swaziland, $1,235); Plains Prehistory (Nebraska, $575); Iroquois Village Culture (Albany, $600); Coral Reef Colonization (St. Croix, $1,l70). Air fare not included.

* University Research Expeditions Program: A smaller version of Earthwatch, this Berkeley, Calif., organization is listing 23 spring and summer expeditions originating from the nine campuses of the University of California. Upcoming summer trips are scheduled to Belize (Mayan archeology, $1,l25), Kenya (monkey behavior, $1,425), Alaska (Arctic flora, $965), Papua-New Guinea (shell evolution in the South Pacific, $1,125). Air fare not included.

Closer to home, three two-week excavations are scheduled in June and July at Flowerdew Hundred, a Virginia plantation site on the James River that has become one of the richest archaeological digs in North America. Living is in a tent camp, and, says the project brochure, expect "hot, humid weather and hard, but rewarding work." Fee, including meals, is $500.

* Archaeological Institute of America: Unlike the first two, which feature a variety of scientific disciplines, this New York City-based professional association serves as a clearinghouse for volunteers in archaelogical research only. It is advertising 75 projects in a catalogue due out this month.

In a similar vein, although not for science, the Sierra Club, a national environment group headquartered in San Francisco, has for 24 years been recruiting vacationing outdoors enthusiasts to help maintain, construct and clean up wilderness trails and campsites in America's national park system. Thirty-six 10-day maintenance trips are scheduled this year. Because participants are camping, the nontravel costs are quite inexpensive.

In Alaska considerable interest has been shown in a restoration project at Denali National Park in August ($220), but in our own neighborhood, the Sierra Club will be repairing side trails in Virginia's Shenandoah National Park June 13-23 ($105). In both cases, the fee includes food and cooking equipment. It is up to the volunteer to get to the trail head, though the Sierra Club will coordinate travel arrangements. The work is often strenuous, but the rewards of shared endeavor and campfire camaradarie keep many participants returning. And there's plenty of time off for exploring and enjoying the landscape.

All four groups see an increasing interest in the kinds of sometimes-arduous trips they offer. Universally, they describe their participants as generally well-educated and often well-traveled. In many cases they are hobbyists--bird-watchers, butterfly collectors, history buffs, frustrated Egyptologists, desk-bound environmentalists--who welcome the opportunity to work closely on site with a professional. On many programs, photographers are especially welcome to record findings. Scuba divers are in demand to explore underwater sites.

James Owens, an assistant U.S. attorney in Washington, and his wife Kathleen, a teacher at St. Elizabeth's Hospital, volunteered their video-taping skills and equipment last month to a University of California at Davis study of carnival folklife in Bahia, Brazil, where the festival is still free of commercialism. It was their second trip capturing the parades and dances, and they are planning to go again. "It's a marvelous trip," says James Owens, who as a result of his vacations is becoming something of an expert on carnivals himself.

In the case of the Sierra Club's projects, the volunteers usually are campers and backpackers "who want to give something back" to America's parks, says program coordinator Kelly Runyon, a mechanical engineer. "We want to do work in the wilderness that would not otherwise get done." On July 15, he's leading a trail maintenance crew to Lundy Canyon in the mountainous Hoover Wilderness of central California, west of Yosemite National Park ($75).

While there's usually a minimum age of about 16 for the four groups, there is no upper limit, and volunteers have signed up in their seventies and eighties. But, says founder Jean Colvin of the Berkeley program, volunteers must be interested in "learning and working" and they must be "flexible and adaptable" to meet changing political or environmental situations abroad. When the animals you are studying move, you have got to be ready to pack up and follow.

Another caution from Earthwatch spokeswoman Blue Magruder: "A lot of projects take place in fairly remote places, but this is not adventure travel. You may be sitting in the bottom of a trench carefully excavating." To some, this may sound tedious, "but you are actively learning. For a person doing it the first time, it can be exciting." If a project takes you to the Great Barrier Reef 50 miles off the coast of Australia, you will be living on a boat "and not even get to go into a pub for a drink."

Anywhere from a half-dozen to 20 volunteers may be needed on a research site, says Magruder, with the average ratio of one professional to about five novices. In many cases, projects have continued for several years, with successive batches of volunteers carrying on the work. The dropout rate tends to be low, since there is a screening process to determine, among other things, physical stamina.

Participant names are kept on file, and when reports of findings are finally published--scholarly studies are slow getting into print--efforts are made to make sure everyone involved gets a copy. In some instances, the volunteers have received credit in professional journals.

If Howard's Margaret Collins is any example, the scholars couldn't be happier about their paying guests. "They are the most durable, cheerful, varied people, with so many special skills," she says. Since 1976, Collins has made about 18 trips to the Guyana site--officially the Kartabo Research Station--studying rain forest fauna ahead of the log cutters. When she retires in a few years, she plans to move to a home she's established there.

Much of her work (and that of the volunteers) involves collecting insects with nets, scent traps and (at night) ultraviolet lights and then observing them. Comparisons are made of what exists before and after the loggers. She credits a couple of her volunteers with devising improved methods of collection, and she delights in a 21-year-old geology student (who she hopes returns) who turned out to be especially adept at meeting with the native people of the interior. Her next trip is scheduled for December (two sessions, Dec. 1-15 and Dec. 16-30), at a cost of $890, not including air fare.

Customarily, up to a dozen volunteers fly with her to Georgetown, Guyana, and then head up-river by boat or small plane. Nights are spent in tents sheltered from the rain by Indian-style thatched awnings. White sand a foot deep makes a dry and comfortable flooring. Dried foods are supplemented with produce from the garden and--since Collins is also a specialist in edible plants--from the rain forest.

Collins, by the way, does all the cooking. On these vacation trips, it's not all work for the volunteers, after all.

For a full list of upcoming expeditions and additional information:

* Earthwatch, Box 127, Belmont, Mass. 02178 (617) 489-3030.

* University Research Expeditions Program, University of California, Berkeley, Calif. 94720 (415) 642-6586.

* Archaeological Institute of America, Dept. WT 53 Park Place, Suite 802, New York, N.Y. 10007 (212) 732-6677. Send $5 for latest Fieldwork and Opportunities Bulletin.

* Sierra Club Outing Department, 530 Bush St., San Francisco, Calif. 94108 (415) 981-8634.