THE FARMERS chose the Monday-morning rush hour for their entry into Washington in order to focus attention on their demonstration. They got the attention they sought, all right, but it is not the kind that is likely to do their cause much good. By creating one of the worst traffic jams in the area's history and by letting violence erupt around the Department of Agriculture, those who drove the tractors and trucks are making few friends among the people who live, work -- and make policy -- around here.

The extent of the disruption that the farmers have already brought to this area invites comparison with only one other recent demonstration. That was May Day in 1971, when opponents of the Vietnam War set out to close the city. The farmers did not say they had such a goal in mind, but the timing of their arrival and the deliberate blocking of highways and streets had the same effect. Workers were delayed or kept from getting to their jobs; police were distracted from their usual duties; emergency vehicles ran the risk of becoming snarled in traffic.

There was one crucial difference. In 1971, the police did their best to keep the city open by breaking up the demonstration and arresting as many protesters as possible. This time the police aided the demonstration by giving the tractor and truck caravans priority on major commuter roads and special routing and parking privileges when they reached the District of Columbia. The difference, in terms of disruption, was hardly noticeable.

It is difficult to see what else the police could have done. There are no minimum speed limits on major highways and no unusual restrictions on tractors in either the District or Maryland. Those who drive tractors on major highways in Virginia must get permits, but these are issued routinely. The federal government could have kept the tractors and trucks off the parkways, but that would have put them onto other heavily used roads. Once the caravans were under way, arresting the drivers who deliberately blocked traffic might have created even worse problems. Handing out tickets is easy enough. But what do you do about the tractors? Hauling these huge pieces of machinery away is not quite the same thing as towing an automobile.

The special treatment provided by the police in all three area jurisdictions -- many traffic violations were simply ignored -- did not seem much appreciated by the farmers. Some of the scenes around the Department of Agriculture as the day went on were also reminiscent of 1971. Tractors chained together, police cars rammed, and tear gas in the air -- these are not the stuff of a peaceful protest.

Now that the city has tolerated one day of disruption, its officials and those in the neighboring states must begin to enforce all the laws. If those on the statute books are inadequate to deal with this new situation, all three legislative bodies are currently in session and readily available. The goals of law enforcement must be, as they were on May Day, to maintain order and to keep the public throughfares open.