President Reagan yesterday nominated William E. Brock, the special trade representative, to be labor secretary and said Brock's primary goals will be to rebuild administration ties to labor and attack "the serious endemic problem of youth unemployment."

Brock, 54, the former Tennessee senator instrumental in reviving the Republican Party after Watergate, succeeds Raymond J. Donovan, who resigned last week to stand trial in a New York court on 137 charges of grand larceny and fraud stemming from activities of his construction company before he took office.

Brock acknowledged yesterday that Reagan's relations with organized labor have not been good.

"Well, we've had some very difficult times, and we have a lot of communicating to do," he said. "I think my primary job is to do whatever I can to create as many jobs as I can."

AFL-CIO President Lane Kirkland said that the nation's largest labor federation "welcomes the nomination" and that, "while we have not always agreed, he has earned our respect." Brock telephoned Kirkland, whom he described as "an old friend," after accepting the job.

As trade representative since 1981, Brock has shown sensitivity to labor's concerns about imports of foreign-made goods. White House officials said they expect that sensitivity to help him build political bridges to the leadership of organized labor, which largely endorsed Democrat Walter F. Mondale in last year's presidential election.

"There are a lot of good ideas in labor on things that we might be able to do better and to try to give them a welcome opportunity to participate, to have a place where they can have a voice," Brock said.

Senate Majority Leader Robert J. Dole (R-Kan.) predicted that Brock would "sail through" the confirmation process. There was no word from the White House about a possible successor to Brock, but spokesman Larry Speakes said Reagan intends to fill the post.

Reagan recently decided against creating a Department of International Trade and Industry that would have combined Brock's office with portions of the Commerce Department.

Brock discussed the Labor post with White House chief of staff Donald T. Regan over the weekend while they were in Quebec for Reagan's meeting with Canadian Prime Minister Brian Mulroney.

Some officials told reporters Tuesday that Brock was not interested in the job. But Brock said that, when Reagan offered him the post yesterday morning, he was "persuasive" and cast the offer as a "challenge that is impossible to resist."

Brock was selected from what Reagan called a "blue-ribbon list of candidates" that included White House political adviser Edward J. Rollins, Reagan's 1984 campaign director.

"Brock is first rate," Rollins said yesterday, adding that Brock could help the GOP attract blue-collar voters, a key part of Reagan's electoral coalitions.

"We probably should have won Minnesota," Rollins joked. "I knew they'd punish me at some time or another for losing it." Reagan carried every state but Minnesota last fall.

Brock earned a reputation as a hard-nosed trade representative at a time of rising protectionist sentiment in the United States and around the world even as he worked under a president ideologically committed to free trade.

Asked whether his goal of creating more jobs would conflict with positions he has taken against trade protectionism, Brock said:

"I don't think so in the least. This country cannot, as an economy, create the maximum number of jobs . . . and achieve the maximum level of growth, deal with inflation, which was the cancer that was costing us jobs, if we have protectionism. That's a contradiction in terms. Protectionism will ultimately destroy jobs in this country, and it is the wrong way to go."

Reagan, who has done well among rank-and-file blue-collar voters but been at odds with the leadership of organized labor, said Brock will reach out to labor, "organized and unorganized." He said Brock, as GOP chairman, had "laid the groundwork for what was one of the great Republican Party victories of quite some number of decades" in 1980.

"He has been a trade negotiator, and anyone who's spent four years dealing with international trade can negotiate with almost anyone," Reagan told reporters.

Brock said it is important that he "stay out of negotiations and let the collective-bargaining process work." He said "a major concern of my own" is the high unemployment level among youth, particularly blacks.

He also predicted that "we're going to have a lot of problems" keeping workers properly trained as the economy continues to shift over the next decade from industrial to high-technology jobs. "And if we can contribute in that area, I think it would be very important also."

Brock would not comment on other Labor Department issues but, asked whether he would continue to push for relaxation of occupational health and safety rules, replied:

"You're asking an area that is outside of my experience of the last four years, and I'd rather wait and see. There is a real value to the safety standards that we have established and, to the extent that we can make them effective and workable and efficient, cost-efficient as well as human-efficient, I'd try to do that."

A spokesman for Brock said the Brock Candy Co. of Chattanooga, run by his older brother, Pat, is non-union. The spokesman also said Brock supported right-to-work laws, which allow workers not to join unions, when campaigning in Tennessee but has not spoken about the issue for many years.