What Joe wants to do most in life is to walk without his crutches," said his mother Mary Thomas.

"He tries so hard. Never say no to Joe," she said with a gentle laugh. But her smile was sad and the expression in her eyes distant, as though the thought of Joe walking by himself was only a tired dream.

Joe was born with cerebral palsy 17 years ago.

As Mary Thomas spoke on a recent ysaturday, she looked across a green field in Upper Marlboro, still somewhat amazed at what she saw. In the field stood Joe, balancing on one crutch and eagerly brushing a big, gentle mare named Katy with his other hand.

Joe is one of 10 handicapped youths from Prince George's County who are enrolled in a pilot, 4-H-affiliated program call Progressive Equestrian Therapy (PETS). The program will offer two summer sessions and already has a waiting list of 20 applicants.

Started May 2, the project aims to help mentally and physically handicapped people adjust to their disabilities through riding. It is one of more than 140 such programs affiliated with the North American Riding for the Handicapped Association (NARHA) that have sprung up around the country since the early 1960s.

A year ago the excited shrieks of happy retarded children on horse-back were just a dream in the mind of Gwen Branzelle, 42, a mother of three who lives in Gambrills, a small town 3 miles east of Fort Meade.

Last June Branzelle got the program off the ground by placing ads in local newspapers and speaking before the Bowie City Council and Prince George's County 4-H Cooperative Extension Service (affiliated with the University of Maryland). She asked for volunteers and donations to help turn her vision into a reality.

Branzelle, however, gives the credit to the 20 other PETS volunteers.

First on her list is John Halterman, who has donated his farm, horses, money and time to PETS.

"He built the mounting stand . . . and he even lets me board my horse here to use for the program," she said.

Then there's the husband-and-wife team of Wayne and K. C. Bergman of Annapolis. He is public relations director for PETS and K. C., who is certified by NARHA's Cheff Center for the Handicapped in Michigan, is the instructor. Cheff Center is the world's largest training school for equestrian instructors of the handicapped.

Today the nonprofit project operates on an annual budget of $800, financed from $1,000 raised at horse shows and raffles and by selling Christmas cards. PETS has four operating committees, about 20 volunteers and a 16-member board of advisers. The free, eight-week courses meet for one hour a week; students enroll through the Prince George's County 4-H Office.

There are just four other similar programs in the Washington-metropolitan area. They are the Maryland Therapeutic Horsemanship Association at the Columbia Horse Center in Columbia, Md.; Riding for the Handicapped Foundation Inc. in Clarksburg, Md.; Carroll County 4-H Horseback Riding for the Handicapped in Westminister, Md., and the Loudoun 4-H Club Riding For the Handicapped Foundation Inc. (affiliated with Virginia Polytechnic Institute's Cooperative Extension Service) in Loudoun County, Va.

None of this, however, has any meaning until one meets and learns the story of Socrates Pappas (his friends call him Sockey), a mentally retarded 11-year-old from Clinton who had never been on a horse until he enrolled in PETS.

It wasn't until he was five weeks into the program that Sockey climbed aboard a regular-sized horse.

In the first class, much to the surprise of Sockey's parents Charlie and Nina, a long-standing fear of heights surfaced in Sockey when volunteers tried to put him on a horse.

After he screamed, kicked and cried for 30 minutes, Sockey was allowed to ride Stumpy, a small Shetland pony.

"I gave up. He didn't want to do it and I didn't want to force him . . . you know, it was hard for us to watch him get so upset," said Sockey's father.

Branzelle described the frustrations of volunteers who "didn't want to let him leave the class. He really liked riding Stumpy and we knew if he could get over the fear of heights that he'd probably love riding the larger horses.

"Finally we told him that Stumpy was sick and that unless he would get on one of the big horses he couldn't ride," she said.

Sockey's father said he was particularly impressed with the way volunteers finally got his son on a horse. "He was more willing the second time, since he had been on the smaller horse, but he still refused. . . . He stiffened up just like a board."

Pappas imitated his son holding his arms stiffly next to his body, then laughed as he continued the description:

"I think it kind of surprised him. They just went right ahead and lifted him up in that rigid position and put him on the horse. Once he got up there he was all right."

It was easy for Pappas to laugh at the memory because at the very moment he was recalling it, Sockey was waving and yelling for his parents to see the maneuvers he was performing -- astride a very bigh horse.

Just two Saturdays after Sockey's first forced ride in the saddle, he had become the most enthusiastic -- and relaxed -- student in the class.

Pappas, who has seen many people try to work with his son, couldn't praise the program enough.

"I think this is the best program of any I've seen because they're more patient and more persevering with the kids. . . . They really care about the handicapped," he said.

The fourth group -- in addition to the students, parents and volunteers -- is made up of members named Wind Song, Katy, Willie, King, Yoska, Blazer and Sugar.

"They've got to be the seven most gentle horses in the world," said Branzelle as she described how Wind Song and his friends were screened for their unusual Saturday-morning duties.

"We had to make sure these horses wouldn't jump at every little thing, like if a car drove by and honked its horn or a piece of grass flew in their faces. So we got them out here and yelled at them, threw things at them . . . some of the volunteers got on them and jumped up and down and kicked their legs."

And what did the horses do?

"They didn't even flinch," said Branzelle.

Whether it's the calm horses, the constant encouragement from parents and volunteers during each session or the determination of 10 young handicapped people, it's difficult to pinpoint the source of the hopeful spirit that seems to reach out to anyone entering the small field nestled in the quiet, rolling hills of Croom in southern Prince George's County.

Maybe the answer best lies in Joe Thomas' reaction to having four strong legs beneath him during the first class nine weeks ago.

"I felt taller. . . . Sometimes (after riding) I felt like I can walk better."