Tobacco farmer Dwight W. Watson was sentenced yesterday to a six-year prison term for making threats, destroying property and paralyzing part of downtown Washington after he drove his tractor into a pond on the Mall last year.

U.S. District Judge Thomas Penfield Jackson told Watson that he was imposing the penalty -- and rejecting several pleas for leniency from the defense -- primarily to stop another civil protester from tying up a large number of law enforcement officers and terrifying a city jittery about terrorist attacks. Watson's siege lasted 47 hours.

"You may not have intended to engage in terrorism, but nevertheless, you did terrify people," Jackson told Watson, 51, who had said he came to Washington from North Carolina to bring attention to the plight of farmers. "Whatever your intentions, this city regarded you as a one-man weapon of mass destruction."

Jackson told Watson that his primary complaints -- that tobacco farmers had been unfairly maligned as purveyors of cancer and were losing their once-honored livelihood because of a government squeeze on the product -- were causes that merited civic protest.

"Mr. Watson, I have concluded you are a nice guy and you had a legitimate grievance . . . which [you] chose to express in a horrendous fashion," Jackson declared. "The sentence I will hand down to you today is intended to deter the next nice guy who thinks he has a legitimate complaint."

Watson probably will serve four years in federal prison. He will get credit for the 15 months he has spent in jail and probably will get another year off the six-year term for good behavior. Had he accepted a plea bargain offered by prosecutors instead of taking the case to trial, his sentence would have been 31 months.

A jury took only 45 minutes to convict Watson of making false threats and destroying government property in the episode, which began at lunchtime March 17, 2003, when Watson drove his John Deere tractor and trailer into a pond at Constitution Gardens and threatened to blow it up with "organophosphate bombs."

The standoff created a furor. Police cordoned off a 10-block area, leading to traffic tie-ups during four consecutive rush hours. Several nearby government offices were evacuated, and a large section of downtown Washington was disrupted. U.S. Park Police and other agencies brought in sharpshooters, negotiators and an armored vehicle in a round-the-clock law enforcement effort that cost an estimated $2 million. Watson finally surrendered peacefully March 19.

What he claimed were bombs turned out to be nothing more than two cans of bug spray.

During his trial in September, Watson told the jury that he never meant to threaten anyone and that law enforcement officials misinterpreted his intentions. The judge told Watson yesterday that he had been "his own worst enemy" in his defense, and the downtrodden farmer, whose gray hair has grown wavy and shoulder-length in jail, agreed.

Watson, whose family had grown tobacco and tobacco seed on 1,500 acres in Whitakers, N.C., for more than a century, received an outpouring of support from members of his rural community. They sent more than 100 letters to the judge attesting to Watson's honesty and integrity. A Web site started by tobacco farmers and family members describes Watson as an "American hero" who called attention to the difficulties of tobacco farmers.

Watson's attorney, federal public defender Erica Hashimoto, asked for a sentence reduction because of Watson's law-abiding history and service as a military police officer. Prosecutors said he deserved the prison time.

The judge said that he was moved by the words offered on Watson's behalf but that they did not change the facts of the case. Jackson agreed to recommend that the prison term be served in a federal facility in Goldsboro, N.C., near Watson's family, or in Morgantown, W.Va.

In court yesterday, Watson apologized to Jackson and the city for the fear and damage he caused.

"My actions were totally uncalled for, totally unacceptable and totally wrong," Watson said. "It was not my intention to hurt anyone, but it looks like I was trying to hurt people. It was foolish."

He added that for five years before the Mall incident, he waged a series of protests of government and industry actions.

Watson's brother, George Watson, who came from North Carolina to attend the hearing, said he and his brother "were hopeful something more reasonable would come down." He said he was disappointed that his brother was viewed as a threat in the capital, which at the time was under heightened terrorist alert.

"My brother was a freedom fighter, not a terrorist," George Watson said.

Dwight Watson told the judge he would not return to tobacco farming after getting out of prison. He then offered some final words before marshals led him away:

"Don't smoke, because tobacco's contaminated, and help the veterans."

George Watson, leaving U.S. District Court with his wife, Deb, said his brother, Dwight, "was a freedom fighter, not a terrorist."Assistant U.S. Attorney Jay Bratt had offered the farmer a plea bargain.