Gerald McCathern, a broad-shouldered farmer from Texas, is the head man in a volunteer organization that has no dues and claims there are no head men.

As wagonmaster of the American Agriculture Movement, he tried -- and failed -- yesterday to command the attention of the farmers he organized.That inability helps explain the sporadic, shapeless and occasionally violent pattern of the tractor assault on Washington.

District of Columbia officials said they spent the day looking for leadership among the thousands of farmers in the demonstration. They wanted someone from the farmers' organization who could negotiate "accommodations" that would allow the farmers certain predesignated routes for their caravans and at the same time leave the city open for ordinary traffic.

They didn't find it.

McCathern had led a caravan of 200 tractors into Washington when he encountered a mob of farmers who were slamming the hood of a police car with their fists and cursing.

Entering the crowd at Third Street and Madison Drive NW, McCathern screamed: "I'm the wagonmaster, I'm the wagonmaster."

A policeman on horseback gave McCathern a puzzled look. The farmers he is supposed to lead ignored him.

Earlier, as he led an eight-mile-long caravan of tractors and farm equipment into the city before dawn, McCathern said of his organization's members. "We are all equals." He had not, he said, asked to be the wagonmaster.

"I was the first one last summer to start talking about bringing the tractors back [to Washington]," said McCathern, who raises wheat and corn in Hereford, Tex.

"If you open your mouth, you get a job," he said as he drove his $32,000, 15,000-pound International tractor toward the city.

He added that the whole idea of protesting bothers him.

"It's asinine that we have to come here. Tractors don't belong in the city. We realize we are going to inconvenience a lot of people, but it's better to wait in traffic jams now than wait in line for food in a couple of years."

McCathern said he has not made any money on his 520 acres since 1975 and that he is one of thousands of food producers who are going broke. To avert that, he said he was willing to lead tractors into a city where they cause nothing but trouble.

After going to bed at midnight, McCathern got up at 3 a.m. to warm up his rig and fight the first battle of the day -- the struggle for a clear channel on his CB radio so he could tell the tractors behind him where to go.

"Clear the channel for the wagonmaster," McCathern called again and again as tractors belched diesel fumes into the bitterly cold predawn air.

The tractorcade pulled out from Bull Run Regional Park in Fairfax County about 23 miles west of Washington at 3:30 a.m., and from the beginning McCathern had trouble keeping the farmers in line.

At 3:45 a.m., McCathern called for the farmers to get off Channel 14 and told them to look out for late-comers who were driving to the park to join the tractorcade. "Why didn't they get up and out like they was supposed to," came a reply on the CB. McCathern said nothing.

The wagonmaster looked frequently through a rear window smeared with 1,800 miles of road dirt to see if the caravan was keeping together. It did not keep together and McCathern was forced to slow to 10 miles an hour.

When the tractors were forced by police to wait 30 minutes on the Capital Beltway, insubordination on the radio turned to mutiny on wheels.

"Hell, let's get going," a driver from Missouri said over his radio. McCathern tried to explain that the farmers' complaint was with the president and Congress, not the Virginia State Police.

"If you're not goin', Missouri is pulling around," came a reply. Three Missouri tractors took off.

McCathern swung his tractor across the Beltway and cut off the three renegades. A state police sergeant, seeing the farmers' impatience, quickly told McCathern to lead the tractors across the highway onto the George Washington Memorial Parkway.

Seemingly infected by the Missourians' militance, McCathern drove down the center of the parkway, preventing other traffic from passing and forcing commuters who had come to the parkway early in hope of beating the tractors to become part of the protest.

The wagonmaster said the Missourians "are pretty sincere" and explained that four of their friends were killed in a plane crash in December on a flight to protest farm prices that was bound for Plains, Ga.One of the tractors from Missouri flew four black flags.

McCathern then had to warn other farmers against using their radios to curse CB-equipped commuters who were cursing them.

The tractorcade passed beneath Key Bridge at 6:15 a.m., just as the cloudless sky over Washington turned a reddish white. McCathern slowed to seven miles an hour and turned up the AM-FM stereo radio in his cab. A disc jockey said the farmers aren't getting any sympathy from the people of Washington.

"I pay taxes. I can drive on these roads. This is a business trip for me," McCathern said, turning his tractor up the ramp to the Roosevelt Bridge. On the bridge the tractors spread out, a Klamath Falls, Ore., rig to McCathern's left, a Missourian to his right.

The procession slowed to a crawl. A voice on McCathern's CB said, "This Washington traffic is so bad we just can't drive in it. The wagonmaster smiled. CAPTION:

Picture 1, Policemen raise their clubs against protesting members of the American Agriculture Movement outside the headquarters of the Department of Agriculture. By James A. Parcell -- The Washington Post; Picture 2, Protesting farmer gives policeman some of his thoughts in confrontation at Third Street and Pennsylvania Avenue. By John McDonnell -- The Washington Post; Picture 3, GERALD McCATHERN... "I'm the wagonmaster."