The tree farmer from Virginia drove to the nation's capital with his wife two weeks ago, settled in a hotel room paid for by a lobbyist and spent a few extra minutes deciding which tie to wear the next day.

John Burke was a witness -- a Washington witness. When morning came, he reconsidered his tie choice, opting for one with a black and gold pattern, then went to Capitol Hill. From his reserved seat, he watched carefully as two dozen members of Congress grilled the undersecretary for natural resources about restoring money for a forestland conservation program.

The 50-year-old tree farmer, coached but still a bit nervous, was third in line for the spotlight. "I was trying to gauge whether I was going to get questions like that," he said later.

At the hearing, held before the House Committee on Agriculture, Burke served the role of ordinary witness for his pet cause: trees. Burke, a lawyer who manages 2,000 acres of pine and hardwood in Woodford, about an hour south of Richmond, became another voice in the process of governing.

On any given day when Congress is in session, a dozen committees can meet to investigate wrongdoing, oversee government departments, check up on federal laws and solicit opinions on legislation. Burke and others like him play a crucial role in the sometimes enlightening, sometimes numbingly tedious process by which government exercises oversight.

The arrival of an ordinary witness in Washington is usually the result of careful choreography, a selection process that combines old-fashioned offerings from interest groups and high-tech Internet searches with studious vetting. Some are coached; others know their lines from the start. All end up in a stiff-backed chair subject to a chairman's gavel and a host of rules of engagement, their experiences differing vastly, depending on the subject.

"I've seen little old ladies get very nice treatment, and I've seen little old ladies get very rough treatment," said Rep. John D. Dingell of Michigan, the ranking Democrat on the House Committee on Energy and Commerce and its former chairman.

Before Burke sat in the witness chair, he was told to pay attention to a small digital clock that limited his time to speak. When it was his turn, he forgot to turn on the microphone. A staff member flipped the switch. As the clock's light kicked from green to yellow but before it turned red, Burke made all his major points:

That family-owned forestland like his helps protect watersheds and wildlife. That America is losing 1.5 million acres of forestland each year. That tree farmers need the funding from the conservation program to better protect, restore and manage their land.

"There's a certain amount of healthy nervousness," Burke said, describing the hours of preparation for five minutes of testimony. "You have to have a certain amount of anxiety to be on."

Hearings can range from highly political to unusually bipartisan, as was the case with Burke's hearing, where members on both sides of the aisle fought the administration's attempt to shrink a program funded by Congress. At other times, the points made by a witness are casualties of the verbal dueling between members.

James Warren, a truck driver from Rutherfordton, N.C., didn't do much to prepare for a recent hearing on contracting in Iraq. The former driver for Kellogg, Brown & Root showed up in short sleeves and khakis, with this goal: to prove that trucks aren't being maintained properly, that money is being wasted and that lives are at risk.

But the House Committee on Government Reform had other plans. In between shuffling notes and coming and going in mid-testimony, the members accused one another of playing politics. The trucker was caught in the crossfire over Halliburton Co., the KBR parent formerly run by Vice President Cheney.

Nobody seemed very interested in discussing truck maintenance.

"It was more theater than anything," Warren said.

Warren and Burke wound up at the witness table after a series of calls by congressional staffers. The staff set things in motion by word of mouth and calls to lobbyists and industry groups. They use the Google search engine on the Internet to find experts and check newspaper articles to see who is drawing media attention. In the case of Warren, media reports about truckers complaining of waste reached the committee's minority staff.

Some aides say that one of the smartest moves is inviting speakers from the committee members' home states. A representative is more likely to pay attention if a constituent is pushing incentives to telecommute or demanding exemptions from the phaseout of a hazardous chemical used on fruit and vegetable crops.

Once witnesses are identified by the staff of a committee, they must still pass muster as effective speakers. Success often depends on how close a witness can stick to the message. Members of Congress, while capable of filibustering for hours, appreciate witnesses who are succinct.

Committees sometimes vet witnesses over the phone. When the stakes are high, a committee chairman will often ask for face-to-face interviews. Even when a hearing is not expected to generate fireworks, the parties tend to follow a script. Burke went over his testimony in advance with a colleague from the American Tree Farm System, a program of the nonprofit American Forest Foundation that aims to promote the growth of renewable forest land.

Some committees pay for airfare and hotel costs, especially if a witness has to be pre-screened. Burke was an American Tree Farm System guest -- he is a volunteer and serves as a committee chairman in Virginia.

But many pay their own way. First-time witnesses especially consider it an honor to testify before Congress and often foot the bill. They bring relatives, ask staffers to snap their photograph and stop by the souvenir stand on the way out.

Vanessa Bogenholm, an organic farmer from Watsonville, Calif., paid $405 to fly to Washington the day before testifying before the Energy and Commerce Committee's subcommittee on energy and air quality.

"I left San Jose at noon. I stayed at the Red Roof Inn for $150. And I'm leaving tonight at 6 p.m.," Bogenholm said, checking her messages after three hours in the hearing room. It was worth it, she said, because it was important to convince other farmers that there are alternatives to a hazardous chemical often used to protect crops.

Bogenholm was testifying for the first time, but she is accustomed to public speaking. For novices, there is coaching.

"I urge them not to look down as they read their names and say, 'Good morning, Mr. Chairman,' " said Laurence Wiseman, president of the American Forest Foundation. "That much they should know."

Extra care is taken with so-called victim witnesses, parents who have lost a child or those who have a disease. But whether a witness is considered fragile or not, staff members try to be solicitous, because the process is so intimidating. First-time witnesses are sometimes shown the hearing room in advance. They are gently prodded to speak directly to the members and to interrupt when necessary.

"If they were nervous about screwing up, I would assure them they know more about the subject than any member sitting on the dais," said Michael Barrett, a consultant who helps prepare witnesses under investigation by Congress. For 10 years, he was chief counsel for the oversight subcommittee of the House Committee on Energy and Commerce.

Witnesses can also be pawns in a power play. When Democrats feel they are being treated unfairly, they can threaten a mini-hearing with their own witnesses.

"It's natural for members of different parties, particularly in an election season, to have opposing views. When they do, the committee process will naturally highlight those differences," said former representative Norman Lent Sr., a Republican from New York who was the ranking minority member of the Energy and Commerce Committee when Dingell was chairman.

Most of the battle is for equal time, and when things get nasty, the losing side can end up watching witnesses testify during dinner, long after the news media have left.

Jane L. Delgado, president of an organization of Hispanic health professionals and an old hand at testifying, appeared before the Senate Special Committee on Aging last week and praised the working relationship between its Republican chairman and Democratic ranking member.

But being a witness also has its perils. Delgado once took her daughter to what she thought would be a routine hearing on generic drugs versus brand names. Big money was at stake.

"They were vicious. They must have taken their viper medicine," said Delgado, chief executive of the National Alliance for Hispanic Health. "Afterward, my daughter said, 'Mama, they were mean to you.' "

Tree farmer John Burke traveled from his Virginia property, above, to testify about his pet cause.James Warren, left, David Wilson and Marie deYoung are sworn in before testifying to a House committee about Halliburton Co.'s role in Iraq. In Woodford, Va., tree farmer John Burke walks through the swampy area of his land with his three yellow Labrador retrievers.James Warren, a truck driver, talks to the House Committee on Government Reform about operations in Iraq.