Missoula, Mont. — Jumping out of an airplane into a burning forest in western Montana may not be everyone's idea of a rewarding job, but Linda Reimers likes it just fine. ''People keep asking me why I wanted to be a jumper,'' she says, ''and I say, why not? Maybe we're all a little crazy. It's probably the biggest challenge I've faced, both physically and mentally.'' Ms. Reimers is a rookie smoke jumper , one of seven women who are part of the US Forest Service's (USFS) most elite firefighting force.During the spring-to-fall fire season, the USFS employs about 400 people as smoke jumpers, most of whom are stationed at the Smokejumper Center here. ''Who jumps?'' Ms. Reimers asks. ''We've got schoolteachers, a lawyer, an architect, ski bums. It's as varied as you can get. That's part of the appeal, you're always with different people.'' She herself recently graduated from Montana State University with a degree in filmmaking.Since its beginnings in 1939, the operation has sprouted satellite bases in Idaho, Oregon, New Mexico, and Alaska. Women leaped into the organization in 1980. ''Having women jumpers is a big change,'' Ms. Reimers says. ''Most of the men have adjusted to it. I have an exceptionally good working relationship with most of them.''Dispatching the smoke jumpers as the initial attack unit on a small forest fire can be more economical than sending in district fire crews by helicopter or tanker truck. Time saves timber - smoke jumpers can be in the air in about five minutes.Smoke jumpers parachute near a burning area to put out the fire before it spreads. Most forest fires in the West are caused by lightning and most burn an acre or less, a size easily handled by two or three firefighters.Using a Pulaski, a combination ax and hoe, jumpers ''cut fire line''; that is, clear away trees, shrubs, and earth down to mineral soil, making a shallow trench around the fire to contain it. This process removes the fuel source from the fire.Once the fire line completely surrounds the burning area, the jumpers ''mop up'' by dousing with dirt and water the hot spots inside the line. When only a smolder remains, smoke jumpers strap about 100 pounds of gear - chutes, tools, equipment - onto their backs and hike to a pickup location.Fighting fires can be dirty and arduous. Completing the task may mean working shifts of 18 hours or longer. During a normal six-month fire season, each jumper averages nine jumps, earning enough money for a winter of skiing or going to college. ''One myth of the job is that you make a lot of money,'' says John Harper, who's jumping for his 14th year. ''That's not the case when you consider the hours we put in . . . 300 hours of overtime.''For Ms. Reimers and the other rookies, the hard work began long before the first parachute unfurled. To qualify for the Smokejumpers, each applicant first must have experience on a district fire crew, where he or she learns the tools and techniques of firefighting. As a college student, Linda spent three summers on a district crew. Encouragement from her supervisors prompted her to try out for the Smokejumpers.''The tough part is getting in good shape,'' Reimers says with a smile. ''I lifted weights and ran from November to May to be ready'' for a series of rigorous physical-fitness exams that would warm the heart of a Marine drill instructor.She shook her head as she recalled the day of decision last spring. It began with a 11/2-mile run, followed by a series of sit-ups, push-ups , and pullups. Digging fire line for 14 hours was the next trial, after which all the applicants each packed 90 pounds of gear through mountainous terrain. Some dropped out; Ms. Reimers didn't.Those who successfully completed the initial test then spent a week climbing telephone poles, jumping from towers, and handling parachutes - all part of a simulated parachute jump and landing. The specialized training is necessary because smoke jumpers must land in a variety of terrains, most often in trees.The final qualification was making seven actual parachute jumps. Of the 13 people who started the week with Ms. Reimers, nine completed the program.Linda smiled as she described her first fire jump, made this past summer in Alaska. With her she carried two parachutes, 65 pounds of gear, and a ton of apprehension.''Let's say I was a little nervous,'' she says. ''I said a silent little prayer for a clear head, jumped, and then concentrated on steering my chute. I only thought about what was happening at the moment.''She met the tundra with no problems, helped other crew members handle the fire, and found ''that all the training really pays off. It went pretty smoothly.''Three months and four jumps later, she has found her apprehension has evolved into anxious expectation.''Linda's a very level-headed jumper,'' says Smokejumper superintendent Larry Eisenman. ''Her performance has been up to par for a rookie jumper compared with other people we've had in past years.''When she's not airborne, Ms. Reimers, like the other Missoula jumpers, works at the Smokejumper Center. Some do landscaping at the center, others pack and repair parachutes or sharpen tools. This past summer she worked on a film script for the Smithsonian Institute.''I hope to do more film when the fire season ends,'' Ms. Reimers says. ''It fits into my schedule now to do what I'm doing.''