DINOSAUR NATIONAL MONUMENT, Utah (AP) _ Two weeks of days crouched on a sunbaked, dusty hillside, picking at bits of rock. Squinting into a microscope at endless grains of gray rock, looking for bone fragments and tiny teeth.

Two weeks of nights in a tent. Cold and cold running water nearby.

This is a vacation?

''It was the most fun I have ever had,'' said Jennie Mae Tucker, 79, of Jackson, Miss. Tucker was one of 24 people from across the country to dig for 140-million-year-old bones and teeth of tiny mammals as part of an Earthwatch expedition led by University of Nebraska-Omaha professor George Engelmann.

Earthwatch, a non-profit organization based in Watertown, Mass., bills its programs as a combination of patronage and participation, giving experts and enthusiasts an opportunity to work together. Volunteers pay to work on the research projects around the world.

Tom Hersch got some good-natured ribbing from fellow workers on a St. Louis factory production line after he decided to volunteer. ''They couldn't believe I was paying to go somewhere and work for two weeks,'' Hersch said.

This was the third year Engelmann has led expeditions to Dinosaur National Monument, a partnership that's proved profitable for his research.

''There's no doubt they help to get the material. I can get other grants, but I couldn't get the people. But it's not just that,'' he said. ''There's a value in the experience, the education. It's the most effective way to show how paleontology works, how it affects real life. The more people find that out, the better off paleontology is.''

The volunteers experience all aspects of fieldwork: tedium, frustration when finds are few and far between and rustic conditions.

''We were in a beautiful setting if you didn't mind roughing it,'' said Miss Tucker, a veteran of seven other Earthwatch trips. She has studied whales and leatherback turtles and dug mammoth teeth from St. Croix to South Dakota.

''The scenery was out of this world. There are no words that I can string together that can tell you what it looked like.''

Dinosaur National Monument boasts a fossil quarry and more than 200,000 acres of canyons and desert dotted with sagebrush and juniper trees. Canyons and the Green River surrounded the volunteers at the site, a half-hour's drive from camp on dirt roads. Teams of four alternated in the hot sun or peering into microscopes for tiny mammal teeth at the monument lab.

''Most of the time I didn't have any idea of what I was looking for,'' said Miss Tucker, who did discover teeth among the grains of dirt and rock under the microscope, and a large, perfectly preserved dinosaur tooth at the site.

''The lab I found less exciting, but whenever my eyes would start crossing, I'd go do something else.''

Sue Sebok always wanted to go on a dig, and the western site intrigued the 21-year-old lab technician from Milltown, N.J. ''I really didn't know what to expect when I signed up. I couldn't believe the scenery,'' she said.

''The scenery and the people were the best parts,'' Miss Tucker said.

Sebok said she found out a lot about herself as well as finding parts of crocodiles from millions of years ago.''I learned I can go out and do things on my own. What I learned about geology, dinosaurs - I learned more in two weeks than I could have in a whole semester in school.''