The room where the Senate Appropriations Committee meets is tiny - the better to keep the public at bay, one surmises - and the line outside the door was long, but the farmers from Tennessee were not deterred.

In this vignette of political guerrilla warfare last week, the farmers had stationed sentries along the approaches to Room S 126 in the Capitol to ambush their senator, Jim Sasser (D.-Tenn.).

Sasser was on his way to S-126 to play out his role in a curiously dramatic battle that is making a shambles of legislative process - the flight over the Tellico dam project in Tennessee.

The first to spot Sasser was S. A. McCall, 75, of Greenback, Tenn., a feisty gray-haired woman whose 90-acre farm would vanish if the Tennessee Valley Authority is able to complete the controversial Tellico project.

"We cornered Sasser - if he'd fainted, he couldn't have fallen down," she said. "He let on like he had never heard of us . . . wondered why we hadn't contacted him."

Dan burgner of Greenville, Tenn., head of the East Tennessee Valley Landowners Association, was there, too. "That tends to get my dander up," he said. "Why, I've been in Sasser's office at least twice on this matter."

Sasser heard them out during that hallway encounter, the Tennesseans got back in the line (they never got into the room), and Sasser went on into the meeting to make certain the committee did not try to stop Tellico.

Lobbyists from the White House, which opposes the Tellico dam, were inside the room, too, but unable to persuade any committee member to challenge Sasser. So much for presidential clout.

Without a question being raised, the committee approved the appropriations bill that directs the TVA to complete the dam project on the Little Tennessee River, notwithstanding any other federal laws.

The energy and water-resources money bill is expected to hit the Senate floor this week. Sen John C. Culver (D-Iowa) will once again rise, as he has in the past, to challenge Tellico and, in effect, ask Congress to play by the rules.

This newest episode in the Tellico story may be the most bizarre, involving legislative sleight-of-hand that illustrates how traditional congressional rules of fair play don't always apply when special regional interests are at stake.

The Tellico case became a national cause celebre last year when the Supreme Court ruled that the TVA could not finish the nearly completed project because it had failed to observe the Endangered Species Act.

Completion of Tellico, a $145 million industrial development scheme that would take more than 30,000 acres, much of it prime farmland, also would have wiped out the tiny snail darter fish, which is protected by the act.

The high court ruling set off a flurry of activity by Tennessee legislators who want Tellico finished and by other legislators who feared that the species law could torpedo prized projects in their home districts.

The Endangered Species Act was amended at the urging of Sen. Howard H. Baker Jr. (R-Tenn.) to set up a review panel to decide if controversial projects could be exempted. In its first formal action, the panel this year ruled against Tellico's completion, saying better, more economical alternatives were possible.

Baker was furious. He introduced legislation that would exempt Tellico, as he had wanted all along, and would abolish the review panel that he originally supported.

His Tellico exemption was defeated this year in the Senate Environment and Public Works Committee, and then again on the Senate floor last month by 52 to 43.

With that, the matter appeared closed. The dam would not be completed, TVA would go ahead with its alternative plan, farmers could get their rich land back, the snail darter would live.

But lightning struck on June 18 in the House of Representatives, when consideration of the energy and water money bill was almost completed and only a few members were on the floor.

Rep. John James Duncan (R-Tenn.), who represents the district where Telico would be built, stood to propose an amendment. The clerk began to read, but before he came to the word "Tellico," Duncan moved that the reading be waived.

A reader of the Congressional Record for June 18 will find the amendment and Duncan's explanation of what it would do. In fact, he did not make the explanation, and members on the floor at the moment did not know what he was proposing.

The two key Appropriations Committee members on the floor, Reps. Tom Bevill (D-Ala.) and John T. Myers (R-Ind.), assur ed the House that they had reviewed the amendment and had no objection to it.

Duncan's amendment was passed on a perfunctory voice vote. The official videotape of that day's proceedings showed that, in a span of 42 seconds, without knowing what they were voting on, House members had ordered completion of the Tellico dam project.

The bill went on to the Senate Appropriations energy-water subcommittee, where the Tellico language was left intact at Sasser's behest, and to the full committee last week, where it was greeted by silence.

Zygmunt J. B. Plater, the Wayne State University law professor, who has argued the Tellico opponents' case in the courts, was as astounded by these events as the Tennessee farmers he represents.

"This entire episode makes it clear to citizens - a majority may follow the rules and the procedures, but there always is someone who is willing to short cut on the rules and legislative ethics," Plater said. "These are the ones who undercut the whole system."

"Five years of citizen effort in an uphill fight, plus three years of congressional time and effort, all goes for naught. This breeds a cynicism that endangers a lot more than fish," Plater said.

One result of the Tennessee farm families' journey here last week was that Sasser agreed to meet with them Friday. As the senator ushered them into his office, an aide confided, in an aside to a reporter, that there was no chance that Sasser would change his position on the Tellico dam.