The American Agriculture Movement announced it was coming back to Washington today with tractors chugging in from Virginia and Maryland on U.S. 50, a Capitol rally and lobbying of Congress and the White House.

Predictions of the number of farm vehicles and supporters of the farm strike organizations varied wildly. Some protest leaders claimed 1,000 farm vehicles and 20,000 farmers would come to town for a two-week rally but area police were anticipating fewer than 100 tractors.

Bud Bitner, a movement organizer from Walsh, Colo., said, "This is entirely voluntary and, farmers being as independent as they are, it's hard to predict."

Virginia and Maryland State Police spokesman said the "tractorcades", even, if small, could cause some traffic delays before halting in Washington around noon.

The Virginia group is to start from Warrenton and use U.S. 50 and the Theodore Roosevelt Bridge to reach the city. State police officials said the caravan would be left on its own if it had fewer than about 50 vehicles.

The Maryland group will use U.S. 50 from Davidsonville and take New York Avenue and North Capitol Street to the Mall. The farmers have permits to park 50 tractors on Pennsylvania Avenue below the Capitol and another 400 on Madison and Jefferson Drives between 3d and 7th Streets NW. Any spillover would be parked at RFK Stadium.

The farm group, which called a strike on Dec. 14 to continue until higher prices are achieved, also set a press conference for 10 a.m. today at the Capitol. It holds permits for up to 500 people on the White House sidewalk through Friday and again for Jan. 24-27. They will have to clear out of all areas Jan. 21-23 because of a previously scheduled antiabortion rally sponsored by the Right to Life organization.

Bitner said the farm movement would hold a rally at the Capitol at 12:30 p.m. Tursday and would send a stream of people from as far away as California and Montana in to see congressmen. He said he expected to have 6,000 to 8,000 people here in support of the strike, which so far has had no noticeable impact on farm-product prices.

The American Agriculture Movement held an earlier march on Washington on Dec. 11 that brought far fewer vehicles and people into Washington than had been predicted. The march received heavy media coverage before and during that event.