Caravans of farmers in tractors and trucks began moving along major highways leading into Washington late last night in slow processions expected to cause massive traffic disruption here throughout a day of agricultural protest.

The first convoy -- 88 tractors driven by supporters of the American Agriculture Movement -- pulled out of an encampment at Frederick, Md., at about 11 p.m., heading east along I-70 on a route designed to bring it into the Washington area on U.S. 1. A second caravan of about 500 tractors, campers, pickup trucks and other vehicles left Frederick shortly before midnight, preparing to travel along I-270 and the Capital Beltway toward the city.

Thousands of farmers and hundreds of additional tractors, campers and trucks remained at other take-off points in the Maryland and Virginia suburbs, planning to start off toward Washington by dawn. Since yesterday evening, about 2,000 modern diesel-powered farm tractors and an array of other vehicles driven by American Agriculture Movement members have been parked at these encampments in preparation for this week's demonstrations.

Some of the protesters' plans remained unclear last night and commuters on most major routes into Washington face the prospect of tie-ups caused by the farmers' motorcades.

The tractor-and-truck convoys began moving last night at about 15 miles per hour at the start of a campaign designed to win attention and more money for American farmers.

Leaders of the American Agriculture Movement said they intend to demonstrate peacefully here during the next few days in an attempt to get the White House and Congress to listen to their demands. "We have to do it," said Norman Gingrass, a spokesman for the movement and a Kansas farmer. "We bring the tools of our trade to the capital of the United States where all these laws are made."

The tractor-and-truck convoys appeared substantially larger than the processions that initially brought the movement's drive to Washington last winter. Movement protesters first converged here on Dec. 10, 1977, with about 600 tractors, corn pickers, fertilizer spreaders and pickup trucks. A second smaller campaign took place in January 1978 in an angrier atmosphere marked by a clash with northern Virginia police and a few arrests.

In addition to the main thoroughfares on which the tractors are expected, it appeared likely last night that other routes might also be affected. D.C. police said Independence Avenue between 3rd and 14th streets SW will be closed to normal traffic throughout the day, and that a similar stretch of Constitution Avenue NW may also be closed. Because of the flexibility of the movement's plans, it appeared that no matter when a commuter leaves home or what streets he takes, there is no certainty that he would avoid the farmers.

And with some supporters saying they plan to camp in the city overnight, it appeared unclear how the tractorcades will affect today's afternoon rush hours and tomorrow's traffic.

Asked about the prospects for the afternoon hours, Deputy D.C. Police Chief Robert W. Klotz said, "I imagine it'll be as had as the morning rush hour. Basically this is the same group as we had last year, but twice the size. In my opinion, they have not come here with any grievance against the police or the citizens of the District of Columbia. Their argument lies with Congress, and they think this is a way to get their message across." George J. Berklacy, a National Park Service spokesman, said that "massive traffic problems" appear likely, especially between 1st and 14th Streets NW on both sides of the Mall. The farmers have official permits, Berklacy said, for rallies on the west side of the Capitol for today, Tuesday and Wednesday.

District, Park Service and other police agencies have adopted flexible policies to contend with the farmers' demonstration, including some relaxation of normal traffic and parking regulations. "We have to be flexible -- there's no other choice," said Deputy Chief Klotz. "When you pour 10 pounds of sand into a five-pound bag, you have to accept special conditions."

D. C. Mayor Marion Barry has asked police to be lenient with the farmers.

The Park Service has waived regulations prohibiting farm vehicles and trucks from parking on federal park land and will permit the protesting farmers to leave their tractors along interior roadways on the Mall and around East and West Potomac Parks. "We recognize the crisis, the emergency nature of this situation. We're going to relax those measures to accommodate them," Park Service Spokesman Berklacy said.

Although Deputy Chief Klotz expressed hope that the tractor-and-truck caravans would follow routes designated by police, Klotz added, "If they want to drive anywhere else, it will depend on how many of them there are and what problems it will cause... If they want to drive around the Capitol a couple of times, we're not going to try to stop them."

U.S. Capitol Police have assigned extra officers to contend with the farmers as they converge on the Capitol. Police said tractors will not be permitted on roads within the Capitol grounds. In Virginia, police say the tractorcade will be allowed to use express bus lanes along Shirley Highway and to travel on other interstate Virginia highways this morning. Virginia has not granted the farmers authorization for a return trip tonight or for use of Virginia highways tomorrow, a police spokesman said.

If the protesters wish to return to Virginia tonight or travel on interstate Virginia highways Tuesday, the spokesman said, they will be required to obtain permission from the Virginia highway commission.

In Maryland, state troopers, Montgomery County police and U.S. Park police will accompany a convoy of about 900 tractors and other vehicles from Frederick along I-270 to the Beltway. Maryland authorities said their aim is to keep the tractors, campers and trucks in single file in the righthand lanes of the highways.

Many of the farm protesters spent yesterday attending religious services, preparing for today's motorcade, milling about their campsites and poring over maps of Washington to determine the routes their tractors will follow.

Spokesmen for the American Agriculture Movement said their group, which includes farmers who have come here from nearly 40 states, have one key demand -- obtaining 90 per cent of parity for farm products. Such a shift in farm pricing, government economists say, would add billions of dollars annually to the costs of American farm products. How such a vast change would affect prices paid by customers at supermarkets and grocery stores is a subject of debate, since farm prices form only a small portions of the costs of food sold at retail shops.

Parity, a technical term long imbedded in American farm economics, is a measurement pegged to a comparison of farm prices and living costs today with the agricultural boom years of 1910-1914. Many economists now view the term as obsolete, partly because it fails to take into account major increases in farm productivity over the years. AAM spokesman have reduced their demand from 100 percent of parity last year to 90 percent this year.

Confusion about today's motorcade plans was most evident at a campsite in Frederick. Md., where hundreds of farmers milled about a field that had been churned into a quagmire. While a major convoy of about 900 vehicles remained parked on a farm outside the town, two smaller groups split away and prepared their own plans for heading into Washington today.

One group, including farmers from Nebraska, the Dakotas, Minnesota Montana, Michigan and Ohio, left Frederick Saturday and camped at Greenbelt National Park. "We just want to split into more groups and cover as many routes as possible," Wayne Peterson, a South Dakota leader of the Greenbelt encampment, said "But, of course, there was factionalism. Any time you have 500 people in one place there is going to be dissension -- especially if you have 500 strong people." Greenbelt camp leaders said they had not discussed their motorcade plans with police.

Yesterday, a second smaller group left the Frederick encampment and took up quarters at Cherry Hill Park, south of the Beltway near the U.S. Agricultural Research Center. Leaders said they plan to travel through Prince George's County along Route 650 today.

Amid the confusion, moods varied widely from the encampments in the Maryland suburbs to other gatherings of farmers elsewhere in the area. Some farm leaders promised nonviolent demonstrations and as little traffic disruption as possible, while others discussed measures to take if trouble breaks out.

At Pohick Regional Park in southern Fairfax County near I-95, a group of Texas farm protestors voted to visit the Department of Agriculture today. "Try to avoid starting anything, but I wouldn't back down an inch,"said one member of the group, Marvin Meeks. "If you consider yourself a pacifist, maybe you shouldn't be here."

Members of the Pohick encampment said they already have contacted lawyers in case trouble should occur and one Pohick spokesman, Tommy Kersey, warned his colleagues to "stay in your tractors" if problems arise. "I ain't gonna run, you ain't gonna run, we're gonna be here until we get the job done," he said to thunderous applause.

Yesterday morning, about 900 farm protesters gathered at the U.S. Departmental Auditorium on Constitution Avenue NW for an interdenominational religious service led by Odis Chapman, an Arkansas cotton farmer and Southern Baptist lay preacher. "We're Christian people," Chapman said afterward.

Gerald McCathern, a Texas farmer and a national wagonmaster for the farmers' protest, emerged from the religious service saying, "Farmers aren't strong to demonstrate... The services this morning will place the people in the proper mood as they go out tomorrow -- they are not going out to be destroying anything but to be highly visible and demonstrate peacefully."

Underlying the prayers, preparations and rhetoric was a mood of determination. Leighton Kersey, a Georgia farmer, waited yesterday at the Pohick camp and said he is here for the long haul.

"We're going to stay to the Fourth of July if that's how long it takes," he said.