The American Agriculture Movement's tractor march on Washington to protect low farm prices could create traffic congestion Saturday on U.S. Rte. 50 in Virginia and Maryland and on Constitution and Independence Avenues in the District of Columbia, according to area police.

Estimates of the number of vehicles moving into Washington have ranged from 1,000 to 10,000 farm vehicles. Officials said yesterday that cold weather and predictions of snow were likely to hold the gathering to the low end of the estimate.

The farmer's group, threatening to strike on Wednesday if they do not get higher prices for their crops, now staging vehicles near Chantilly, Va., and Davidsonville, Md., on U.S. Rte. 50.

The Virginia group will come into Washington early Saturday on U.S. Rte. 50, crossing the Theodore Roosevelt Bridge and parking in the curb lane of Constitution Avenue between 23d Street NW and 1st Street NE.

The Maryland group will come from Davidsonville on U.S. Rte. 50 to New York Avenue, down North Capitol to Columbus Plaza Circle to 1st Street NE and then on to Independence Avenue, police said. They will park between 23d Street NW and 1st Street NE.

After a rally on the Washington Monument grounds scheduled to end at 3 p.m., the farmers either will drive their tractors back out of town on the same routes or load them on trucks in West Potomac Park, police said. Police warned that the tractors would move at about 15 to 20 miles per hour on the highways.