Thousands of farmers dined, danced and rallied in Warrenton, Va., last night in preparation for the drive into Washington tomorrow morning in a vast tractorcade of agricultural protest.

After cold days spent heading toward Washington at the wheels of their lumbering farm vehicles, between 3,000 and 4,000 farmers gathered at and nearby National Guard Armory to hear speeches, enjoy a festitve meal and dance to bluegrass music.

Most of the farmers at the Warrenton rally had come from western and southern parts of the nation and were encamped in Northern Virginia at Bull Run Regional Park and Pohick Bay Regional Park.

Their leaders met late last night to plan last-minute details of the last leg of their angry journey -- the rush-hour caravan tomorrow into Washington.

Meanwhile, another contingent of several hundred protesting farmers and their families reached their camdpground on frozen soil out side Frederick, Md., while still another group made camp in Greenbelt Park.

By late afternoon yesterday, about 125 people had arrived at the Greenbelt site in more than 60 tractors, campers and recreational vehicles. The route that would be used Monday from Greenbelt to Washington was not immediatley clear.

Lthe farmers in Frederick, part of the American Agriculture Movement, had traveled for days and nights through miles of small towns, narrow highways and snowdrifts. Their tractors and the farmers bore messages ranging from homilies about the wholesomeness of farm life ("These are deep-rooted Christian people," said a Michigan farmer) to warnings about the Trilateral Commission, a group of 200 leaders from North America, Europe and Japan formed by banker David Rockefeller in 1973. "Why doesn't the media ever tell us about the Trilateral Commission?" complained another farmer.)

But mostly the farmers said they came to talk about the difficulties of making a living farming.

"A lot of people bucked a lot of elements to come here," said Ken Harris, a farmer from north of Lansing, Mich. "It's worth it to save their family farms," he said.

Harris was one of a group of 25 farmers from DeWitt, Mich., who made the nine-day trip together to argue for better farm prices. "We've been cooking for a whole county," said Trudy Miller, one of two women who had made the trip with the group, often rising at 4 a.m. to cook breakfast for the men.

Miller and her husband had been joined yesterday morning by her parents and her 2-year-old daughter. Muller's parents, Harold and Betty Lietzke had driven all night from DeWitt with their granddaughter to join their neighbors for the weekend.

The Lietzke family said they raise alfalfa on about 400 acres, dry it in a dehydrator and then sell it to feed companies. "We're a family farm, 3 family corporsation," Lietzke said.

While their granddaughter slept surrounded by a jumble of clothes and bags of apples, her mother and another woman cooked lunch in the camper parked alongside rows of Cases, John Deeres, Allis Chalmers and other tractors.

Lietzke, Bob Jones, Harris and other farmers from DeWitt stood in the frozen field by the trailers and trctors and talked about the cost of farming. Harris works as a tool-anddie maker at an Oldsmobile plant, in addition to farming. His wife drives a school bus. "You work to support your farm," said Harris.

A recent survey in the Michigan county where he farms found that more that half of the 1,600 farmers there had off-farm jobs, he said. "If they'd give people parity [farm prices which the farmers say would allow them to recover their costs plus a reasonable profit], it would open up jobs for others," Said Harris.

"I've worked in a shop to save a farm," said Lietzke. "I'm a third generation farmer. Our kids are a fourth. Our grandaughter will be a fifth."

The farmers' Frederick campsite was a field on an old farm that is slowly being claimed by the highway department. Frederick County farmer Edward Mercer, who is not part of the American Agriculture Movement, let the farmers stay on the land that he rents and farms that his family once owned.

The farmers were earnest but subdued as they wandered from vehicle to vehicle talking about their plans for tomorrow when they will join tractor caravans from two Virginia campsites and move toward Washington in the morning traffic rush. Many were clearly weary. Don Mollohan from Otis, Colo., had stopped in a small town near the Maryland-West Virginia border Thursday night to get gas and had broken the starter on his tractor. "There were no parts in that town," he said.

After he got on the road again, lagging behind his group, he had slid into a ditch when he stopped to assist a car that apparently had stuck in a snowbank. With several assists from snowplows, Mollohan made it into Frostburg, Md., about 2 a.m. Friday morning. At 6 a.m., he was up again and on his way to Frederick.

When he had arrived finally Friday afternoon, "I shut her down and went to sleep," he said. It had been tough, he indicated, but no tougher than normal life. "I've been out after stock a lot of nights like that," he said.