“Bill Rogers has got — to his credit it’s a decent feeling — but somewhat sort of a blind spot on the black thing because he’s been in New York,” Nixon said. “He says well, ‘They are coming along, and that after all they are going to strengthen our country in the end because they are strong physically and some of them are smart.’ So forth and so on.

“My own view is I think he’s right if you’re talking in terms of 500 years,” he said. “I think it’s wrong if you’re talking in terms of 50 years. What has to happen is they have to be, frankly, inbred. And, you just, that’s the only thing that’s going to do it, Rose.”

These tapes, made in February and March 1973, reflect a critical period in Nixon’s presidency — the final months before it was “devoured by Watergate,” said Timothy Naftali, the executive director of the Nixon Library.

Mr. Naftali said that there were now only 400 hours of tapes left to released, and that those would cover the final months before the tape system was shut down in July 1973 after Alexander Butterfield, who was a deputy assistant to Nixon, confirmed its existence to the Watergate committee.