Russell Grider, a rancher from Floyd, N.M., who came to Washington four times last year to protest low farm prices, sat yesterday in a cold trailer in Bull Run Regional Park in western Fairfax County and said he hated to be back.

"For us, this is just like coming to Vietnam. We don't like those cold showers. It's no fun driving a tractor for eight days on the road -- this ain't no joy ride," Grider said.

Grider is one of an estimated 1,300 farmers at the Bull Run site, and at Pohick Bay Regional Park in eastern Fairfax County, who are preparing to cross the Potomac Monday morning with 700 tractors during the District's rush hour.

Another 1,000-tractor contingent from the West and Midwest is expected to arrive in the District via Maryland at the same time, protest leaders said yesterday.

Gerald McCathern, national wagonmaster of the farmers' American Agriculture Movement, said two of the tractorcades probably would enter the District over the 14th Street Bridge. The route of the third tractorcade has not yet been decided, he said.

The farmers say they will drive their 15-mile-an-hour tractor caravans into the District each morning and out again in the eveings until they get what they want -- assurances from the federal government that farm prices will keep pace with the rising cost of living.

At Bull Run Park, 23 miles west of Washington, where about 300 farmers rolled in on Wednesday, Grider is sharing a trailer built to sleep four persons with eight other farmers from Floyd.

Grider and other farmers at the site, where a hard cold wind yesterday kept nearly everyone inside trailers, said they have returned to Washington because they felt the country still hadn't heard that they are going broke.

Hershel Johnson, a 58-year-old wheat and milo farmer from Arnett, Okla., said he drove his red, white and blue 1964 Ford tractor 1,800 miles to Washington to tell the Congress that "we farmers have been paying out of our pockets for the privilege of growing your food."

The farmers crammed their giant tractors into a parking lot near the park's swimming pool. One tractor was hooked to a trailer on which sat a white outhouse with the slogan "Carter is a Parity Pooper."

Parity is the point at which prices for farm products keep pace with the costs of other products and services, thereby assuring the farmer a constant standard of living.

At the "Parity Hilton," a 40-foot refrigerator truck converted to sleep 10 with a stove, refrigerator and shower, the group from Ropesville, Tex., said they are doing just what they do at the Ropesville Cafe when they gather at predawn for some of Dorothy's coffee.

"We're griping and complaining about the situation we're in and crying on each other's shoulders," said Alvin Ryals, 64, a cotton and milo farmer who huddled over the burner to warm his hands. "We're in the midst of a depression."

Glenn Thrash, a Lubbock, Tex., farmer wearing a black Stetson hat, passed around a copy of a 1948 Lubbock Avalanche-Journal newspaper that quoted a price of $4.33 for a bushel of sorghum. It now stands at $.80, Thrash said.

Many of the farmers said they are "more determined" then last year to get what they are after. "They can call us militants because we're doing something, but we're not the burning type," said James KIRKSEY, WHO DROVE HIS TRACTOR 1,800 MILES FROM Ropesville.

"Folks are three times as determined this year as last 'cause we're twice as deep in debt," said Leighton Kersey, of Henderson, Ga. Kersey, a wagonmaster for the Georgia tractorcade, said he would not be stopped from driving his tractor to the Capitol, despite a traffic regulation prohibiting farm vehicles from the Capitol Square area.

"We're going to the Capitol. Damn the law!" said Kersey, as half a dozen heads nodded agreement in the chilled van.

The farmers, under the banner of their two-year-old American Agriculture Movement, said they plan to set up a "farmer's market" on the west side of the Capitol where they will sell small amounts of wheat, hay, sorghum, and cotton to each other at what they say are "parity prices."

At the end of each day they will "sell back" the items and return to the campgrounds, only to return the next day and re-enact the market scene.

U.S. Capitol Police Chief James Powell said the farmers have a permit allowing them to congregate at the west side of the Capitol on Monday and Ruesday, but that the permit does not include tractors. Powell said the tractors would not be allowed near the Capitol, and that barricades would be set up with police standing by.

In a related development, Frank Blackwell of the Virginia Department of Highways and Transportation said yesterday he would send the American Agriculture Mvement a $500 bill for the more than 400 tractors and farm vehicles that passed through the Richmond-petersburg Turnpike toll booth Wednesday without paying.