Eco-Treks : If digging ancient bones or hugging dolphins are in your spring or summer travel plans, now’s the time to book the trip.

“Green travel” or environmentally oriented trips are a rapidly expanding sector of the world’s biggest industry--tourism. Right now is the time to plan, if you want to get in on the good spring or summer trips organized by commercial tour operators or nonprofit organizations such as the Sierra Club. Groups are small, sometimes six or eight people, and the good reservations go fast.

Venturans who have commented on this kind of adventure have used such terms as “great experience” and “neat stuff.” And many have gone ahead to book another trip of this type.

Participating in the Dolphin Intelligence Project at the University of Hawaii was the first taste of eco-tourism for retired Venturans Midge and Pete Sorem. They were paid volunteers in actual research on development of “a common language to communicate with dolphins.” This isn’t science-fiction stuff. It’s real, hard-science research, one of a hundred or so activities available to interested participants in a program called “Earthwatch” (no relation to this column.)

“We were gofers for Dr. Louis Herman, the project director,” said Pete Sorem, who kept asking me: “Have you ever hugged a dolphin?”

I haven’t, but something in his voice made me think I’ve been missing something.

Working with the marine biologists, he said, was a “once-in-a-lifetime experience.” Next year, the Sorems are thinking about going to Australia to participate in a head count of wallabies. “Or we might go to help dig up the Oxford mammoths,” said Pete Sorem.

This should give you an idea of the immense range of experiences on sale in the world of eco-travel or nature travel or, as it is called in travel agency circles, adventures travel.

Another Venturan, Paul Tebbel, environmental education director at Patagonia, the local clothing manufacturer, is a veteran of this kind of travel, which he calls “sharing somebody’s habitat.”

He went to the coast of China, assisting a biologist investigating animal life on some islands near Hong Kong. “How else would I get to see the outdoors or back door of a country except by going with some crazy guy (the professor) who is studying this stuff.”

Tebbel and Patagonia are frequently asked who the good eco-tour organizers are. In the list below are some nonprofit groups he mentioned. I also studied a lot of reference books to see who’s really environmental and who’s just running a glorified dude ranch.

Look through those books yourself. The most interesting one is Mary Davis’ “Going Off the Beaten Path.” Where else could a vacationing environmentalist find directions to a “solar bar?”

Indeed, every building in the town of Soldiers Grove, Wis., where it’s located, is solar heated. And Seaside, Fla., is a brand-new coastal town designed so you don’t need a car. Someone should do that in our county.

In the meantime, for a glimpse of the world--natural or man-made--that will warm your environmental heart, look into some of these organizations or books--now.

TRIP INFORMATION

Recommended nonprofit environmentally oriented travel programs:

* The Nature Conservancy: (415) 281-0423--California, U.S. and foreign trips. Also, many California trips that are low-cost or free.

* Sierra Club Outings: (415) 923-5630--hundreds of California and U.S. trips. Also call their Southern California office, (213) 387-4287 for trips closer to home.

* Earthwatch: (800) 776-0188 or (310) 451-0327--An organization (no relation to this column) that sponsors field research by finding paid volunteers to help environmental scientists around the world.

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For these recommended publications, check your local bookstore:

* “Going Off the Beaten Path” (second edition) by Mary Davis, $14.95, Noble Press (800) 486-7737. Also from the same publisher, “Eco-Journeys,” by Stephen Foehr.

* “The Green Travel Sourcebook,” A guide for the physically active, intellectually curious and socially aware by Daniel Grotta and Sally Weiner Grotta, $14.95, John Wiley Publishers, (800) 982-2665.

* “Ecotravel,” edited by Lisa Jones. The Buzzworm Magazine Guide, $9.95. (800) 333-8857.

* “Earth Trips,” nature travel on a fragile planet, by Dwight Holing, $12.95, Living Planet Press (310) 396-0188. And a magazine, Just Go!, currently the only eco-travel magazine, introductory offer $11.95 per year, (800) 285-5951.

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To double-check the environmental record of a tour operator in advance of booking, contact the eco-travel equivalent of the Better Business Bureau--The Center for Responsible Tourism: (415) 258-6594, organized in 1984 “to change attitudes of travelers and the travel industry.”