Talk show host Phil Donahue had warned the audience that his program featuring an American Nazi and a Ku Klux Klansman contained "incendiary" material, and he wasn't kidding. Midway through the program's local broadcast yesterday morning, a wire burned up at Channel 9 (WDVM) transmitter knocking both the show and the station off the air for 25 minutes.

More than 350 peopled the station when their screens plunged from white racism into white snow, and many of the callers expressed suspicion that the broadcast had been sabotaged. But the station officials said the boom was lowered not by a miscreant but by electrical failure. "It was legit - honest," one spokesman said.

When Donahue himself was reached at his home base in Chicago yesterday, his first reaction was to discount the possibility of human interference even before it had been suggested.

"I'm sure what happened was just a coincidence," he said. "I know we live in a cynical, suspicious age, but who could have been smart enough to anticipate the airing of that program and gain access to the transmitter? It would take an awfully sophisticated terrorist to do it."

Ralph Thompson, director of engineering at WDVM, said the culprit in the case was a device linking the station's main transmitter with a backup transmitter that kicks in when the other one falls. When the link itself blew out, there was no way out to get either transmitter working until it was repaired.

Thompson was asked if the sudden disappearance of Donahue could have been the result of sabotage. "Absolutely not," he said. "There is no question in our mind that was a component failure."

Donahue's daily talk show is televised live in Chicago and sydicated on videotape one week later to stations in 148 TV markets. The guests on yesterday's segmnt were Frank Collin, head of the National Socialist Party of America and an organizer of the recent Nazi march in the Chicago suburb of Skokie, and David Duke, the grand wizard of the Ku Klux Klan.

On the program, Collin referred contemptuously to inferior races" and advocated that blacks be deported to Africa and Jews to Israel. In response to Donahue's questioning, Collin said the Irish could stay, and so could the Indians.

Donahue was asked yesterday if he didn't feel some reluctance about giving air time to such inflammatory eccentrics. "I do have some anxiety about it," he said, but I'm convinced you don't solve problems by repressing unpleasant ideas. Suppression doesn't work. The proof of that is in Russia now," he added, referring to the recent trials of dissidents there.

As a "courtesy" to all guests who advocate a point of view, Donahue posts their mailing addresses on the screen during the program so they can receive inquiries from viewers. Donahue said that "sure, it's possible" that the Nazis and Klansmen might recruit new members through this device, but said he thought it more likely that putting such people on television and letting them talk "makes sure this kind of position will fall of its own weight."

When WDVM returned to the air at 9:25 a.m., Carole Randolp and Dennis Wholey, co-hosts of the local "Morning Break" show, could be seen laughing and giggling in the studio and assuring viewers that the "Donahue" tape had been stopped when the station left the air and that it would be started again so the program could be shown in its entirely. And it was.

"Donahue" is also seen at the same hour in Baltimore on WBAL-TV, where there was no interruption and, a station spokesman said, only "a few more" calls than usual from viewers objecting to the content of the program.