In what he called a "terrible mistake" that could cost him the U.S. Senate election, Republican John Warner has told a Washington television station that as secretary of the navy he "slowed" efforts to further integrate the service.

In a controversial interview with WJLA-TV, Channel 7 - taped Thursday night to be aired at 11:30 a.m. today - Warner said he had opposed efforts by former chief of naval operations Elmo R. Zumwalt in the racial area. The incident promptly escalated when Warner called the station back that night and sought to correct the transcript because, he said, he had misunderstood the question.

WJLA reporter Jim Clarke said he told Warner of a station policy against editing videotape of political interviews, and quoted Warner as saying:

"I think I've made a terrible mistake. It could cost me the election. It could mean two years down the drain."

Last night, as Warner and Northern Virginia Republican women hosted a $20-a-plate "country supper" for some 3,500 people at his Fauquier County estate, Warner sought to minimize the incident while grim-lipped press aides stood nearby.

"I misunderstood the question," he said, "I missed the word 'integrate.'"

Warner did not specifically deny that he had attempted to slow down Zumwalt's efforts toward further integration in the Navy, but he repeated several times that he had a long record of supporting equal opportunity for all people.

"Admiral Zumwalt and I looked at it in a different perspective as to how fast to go," Warner said. "We both had the same goal and we achieved a great deal working together.

"But mind you, there was a war going on and racial tension aboard several of our ships . . . "

Zumwalt, in a telephone interview yesterday from Milwaukee, said there was "nothing positive or negative" that Warner did to block any integration efforts. "it was just a lack of decision," he said, adding that in his opinion Warner was guilty of "gross indecisiveness" as secretary.

"I was constantly pushing him to make decisions," Zumwalt said. "There was a feeling of general frustration. The problems were much larger than the integration question. Warner was unwilling to move in any area, whether it was race, weapons, etc."

Warner was Navy secretary from 1972 to 1974. Zumwalt's tenure as chief of naval operations ran from 1970 to 1974. Zumwalt ran unsuccessfully as a Democrat for the U.S. Senate against Harry Bryd Jr. in 1976.

Warner's Democratic opponent in the Senate race, Andrew Miller, promptly jumped on Warner's handling of the interview and its aftermath.

Informed of it during a campaign swing through Roanoake late Friday, Miller said, "I am shocked to have learned of Mr. Warner's statement admitting he has frustrated equal opportunity for men and women in our country's armed forces.

"Mr. Warner's statement is a most significant development in this race, because his attitude contrasts clearly with my record of complying with the letter and the spirit of the law's assuring equal opportunity for all Americans," Miller said.

At his news conference yesterday at the country supper, Warner said he had so far received no adverse reaction to the incident from black groups. He said his wife, actress Elizabeth Taylor, had attended a meeting of a black church group in Richmond earlier in the day and had been "warmly received."

The television station transcript of Warner's interview showed he was asked the questions: "Do you think you have black support, and why should black voters support you?"

He replied ". . . I think it's essential that Virginia's next United States senator represent all Virginians, and I am confident I will receive a substantial amount of the black vote, because if you go back in my record . . . particularly . . . in the Department of the Navy . . . we adopted new policies which made it possible for blacks to, I think, have a greater meausre of freedom and job opportunity than ever in the 197-year history of the Navy."

Then reporter Clarke asked:

"But Admiral Zumwalt says you slowed his efforts to integrate the Navy."

"No question about it. I don't deny that." Warner replied.

"You did?" Clarke asked.

"I think, let's say that we had a clash on the subject, quite clearly," Warner said. "He wanted to go much faster. But if you look at the track record of achievement during the period of five years, I think that it was a very major step forward . . . It's a very traditional outfit and you just don't take a hard right or hard left. You sort of move it along and gradually change it, certainly in peacetime."

Richard Lobb, a member of Warner's press staff, said he mentioned to Warner after the interview that the candidate had made a controversial statement on integration and Warner was "just shocked."

Clarke said Warner called him back from Washington's National Airport about 30 minutes later and said he had misunderstood the question.

Lobb said Warner had gone to the interview at the end of a long, fast-moving day and "was not as sharp as he normally is, perhaps."

Warner's schedule, as released to the press, indicated only one event Thursday, a meeting from noon to 2 p.m. at the Alexandra Kiwanis Club. Lobb said, however, that Warner had also attended several meetins during the day plus a fund-raiser in McLean in the early evening before going to the taping.

Warner's schedule, since he received the nomination last month, has rarely shown him attending more than two or three events in a day - a sharp contrast with the schedules of most candidates in a Senate race, including Democrat Miller.

Yesterday's difficulty with the interview incident was not Warner's only setback of the day. As the guests at his estate were gathering up their barbecued chicken and beans, rain poured down, scattering visitors under bushes and tables and postponing the speech by the featured guest, Sen. Barry Goldwater of Arizona.