A tractorcade of protesting farmers that caused a massive evening rush hour jam, bottling up thousands of commuters in downtown Washington, prompted D.C. police last night to ban future tractor parades, at least temporarily.

D.C. Police Chief Burtell Jefferson declared that the farmers, members of the American Agriculture Movement, "went far beyond reasonableness." He said police will permit no further tractorcades "until such time as the farmers are prepared to come up with some type of responsible leadership."

The chief's declaration capped a day on which a good natured protest directed at the White House deteriorated into a confrontation in which four farmers were arrested, a billy goat, a bushel of grain and an oil barrel were tossed over the White House fence and traffic was backed up across the Potomac River. The parade of 197 tractors, a steady rain and the remains of Monday's near blizzard combined to trap many commuters in downtown Washington from 4:30 to 7 p.m., police said.

The demonstration, which at its early afternoon start stretched up Pennsylvania Avenue from Third Street to 15th NW, apparently wrecked a rapport the farmers had established with the police following the scuffles and arrests that marked their arrival here Feb. 5.

The farmers arrived on Pennsylvania Avenue in front of the White House, blocking the street, about 1:45 p.m. and soon tossed the grain and the barrel over the fence. The tractorcade was led from the Mall to the executive mansion by 5-year-old Dustin Covey, who pedaled a toy tractor.

The protest, which Deputy D.C. Police Chief Robert W. Klotz said was to last no more than 45 minutes, went on for nearly two hours, visibly taxing police. At 3:30, U.S. Park Police arrested Kevin Placzec, alleging that he threw farm machinery over the fence onto the White House grounds.

"It got out of hand in front of the White House and it never got back in hand afterwards," Klotz said last night at a press conference to announce the ban on tractor processions.

The police persuaded farm leaders to get the tractors moving as rush hour began, and the first 99 were well on their way down Constitution Avenue toward the Mall where police have created an encampment for them, Klotz said, when some of the last 98 broke from line and began tying up traffic. Three persons were arrested on Constitution Avenue near the White House, all for offenses allegedly connected with attempts to run down police officers with tractors.

Three tractors were impounded and Klotz ordered police officers to ride in the cabs of the remaining break-away vehicles to insure that they followed the parade route.

Both Klotz and Jefferson said police had used restraint but the farmers reacted bitterly. "We'll guarantee you one thing, there will be lawsuits," said Leonard Cox.

Jefferson characterized the farmers' behavior as "breaking an agreement." From the beginning, the protest was filled with unscheduled events.

Throwing the grain and the oil drum over the White House fence after the live goat were intended to illustrate the farmers's argument that it took a bushel of grain to buy a barrell of oil in 1972, but it now takes five bushels.

"As long as they don't throw anything harmful, I don't think the Secret Service is going to get upset about it," said Klotz. But Park Police made an arrest and confronted an angry group of farmers later when some demonstrators toppled a 60-year-old threshing machine in the street, dismantling it and tossed its parts over the fence.

"You've got to draw the line someplace," said Park Police Maj. Denny Sorah, and even many of the farmers criticized their fellow protesters. "That's just not right," said Bob Gieswein, a weathered-looking Kansan who helped calm the crowd.

President Carter, who lunched with members of the National Caucus for the Black Aged yesterday, was apparently unaware of the protest, a White House spokesman said. Vice President Mondale watched from inside the North Portico for several minutes, however.

Earlier in the day, farm movement's leaders met with a group of editors and reporters at The Washington Post in what they said was an effort to improve their image and explain their cause, which is basically an appeal for increased farm price supports. National wagonmaster Gerald McCathern, who said the farmers are not getting a fair return on their investment, said the group would continue to lobby for extended crop loans on Capitol Hill.

But, McCathern said, "The chances are we are going to go home empty-handed."

The farmers were joined, mean-while, by a group from Canada and by new arrivals from the United States. "We move in the shadow of the United States," said Elroy Karius, one of the Canadians. "We support their efforts."

The goat was caught by White House guards after it wandered across the lawn. "Last I heard, he was in custody," said a Secret Service spokesman, who added that the goat probably would be turned over to an animal shelter.