Sen. Orrin Hatch (R-Utah) is delivering a 90-page speech on the Senate floor against the Panama Canal treaty.

Gallery visitors come and go. Reporters come and go. Senators come and go. Even Sen. Paul Sarbanes (D-Md.), who is minding the store for the pro-treaty forces, is relieved by Sen. Donald Riegle (D-Mich.).

Practically the only person to endure is . . . Linda Wertheimer. And she doesn't simply endure, she seems to thrive as the debate reaches its 28th day [TEXT OMITTED FROM SOURCE]

"I've heard more of the debate than the senators have, I'm sure of that," she says.

Seated in the front row of the gallery, Wertheimer yesterday welcomed National Public Radio listeners as the historic broadcasts from the Senate chamber resumed. This is the first time a Senate debate has been broadcast live.

She came on after a switch from the Rayburn building, where NPR's Nina Totenberg had been broadcasting the beginning of the Tongsun Park public hearings. Wertheimer quickly caught her listeners up on what Hatch was saying.

People are listening to the debate by the millions; an estimate 14 to 15 million had heard part of it up through the vote on the first treaty last month. And the number of Wertheimer fans continues to swell.

She tells this story. One day, while her sister was visiting the dean's office at New Mexico State, where she is studying, the dean had his radio turned on.

"That sounds like my sister," said Wertheimer's sister.

"That's Linda Wertheimer," said the dean, a Wertheimer fan.

"Then it is my sister."

Wertheimer smiles. "I guess the dean was a little astounded," she says.

Other listeners with a special significance for her have offered congratulations on her coverage. Janet Murrow, Edward R. Murrow's widow and a member of the NPR board, sent her a complimentary letter. The same day Pauline Frederick came into the NPR offices on M street and congratulated her. Ed Murrow on radio and later Pauline Frederick reporting on television from the United Nations were Wertheimer's heroes when she was growing up in Carlsbad, N.M.

She listened to radio as a youth because there was no television signal in Carlsbad. She says when she was about 15 - she's 35 now - a TV tower was finally put up. But one cold day it iced over and toppled to the ground, leaving Carlsbad without television a while longer.

She went east to college, to Wellesley, and through an exchange program involving the school, got a job after graduation in 1965 with the BBC in London, as a production assistant. From there, she moved to WCBS radio in New York, as a producer. Nine years ago, she married Fred Wertheimer, a vice president of Common Cause, and moved to Washington.

In 1971, finally she got on the air - with NPR.

Looking back, she says it's probably just as well it took a while. "Age makes your voice richer," she says, "so when you turn 30 you're in better shape than when you're 23."

Her reporting from inside the Senate chamber not only has been a broadcasting first but also her most taxing assignment by far. She's been on the air almost 200 hours, some days from 10 a.m. to 7:30 p.m.

At the end of the live broadcast, she jumps into a car driven by her engineer and is taken to the M Street studio, where she hurriedly prepared an hour-long wrapup which she co-anchors with Robert Siegel starting at 9:30. One cluttered office has a piece of paper stuck to the door inscribed "Canal Zone Room."

To survive this ordeal, she's gone into a kind of training. "It takes not just endurance but concentration," she says. "I eat high-protein breakfasts. Steaks, chicken. During the day I take breaks for five or 10 minutes every once in a while. I live off slices of pound cake and Coca-Cola. I bake angel food cakes with lots of eggs."

But because political reporting is what she's always wanted to do, she hasn't tired of the routine."It's a fortuity for me," she says. "I suppose there are those who would find it a torment."

There is repetition - "When some senators take up certain themes you feel you could deliver the speech yourself." And the broadcasts have lengthened the debates because senators have wanted to explain things for the listening audience. "Once, a 'secret session' was proposed," she says, "and Birch Bayh went into a long discussion of what that meant, so people wouldn't think it was a coverup."

But she thinks the broadcasts have made the issues clearer to a wide audidence.

The broadcasts also apparently have made an impression on at least two television networks. Wertheimer says she's had "a couple feelers. I wouldn't like not to take a step were it there to be taken," she says, but she's happy where she is.

Yesterday, when she passed back to Totenberg at the Park hearings, Hatch was still talking. Last night she would have the pleasure of boiling him down to one hour for the wrapup show.