Constance Horner, the director of the federal civil service and the highest-ranking woman in the Reagan administration, has emerged as the leading candidate to succeed William E. Brock as labor secretary, White House officials said yesterday.

White House aides submitted Horner's name to President Reagan for his approval yesterday afternoon, and he was expected to decide quickly.

Brock announced his resignation in a morning departmental news conference, and, in the process, made a campaign speech for his new boss, Sen. Robert J. Dole (R-Kan.).

Brock said he was resigning on Nov. 1 to run Dole's campaign for the presidency because Dole's "extraordinarily personal leadership" made Brock's decision "imperative."

"I am deeply concerned about the enormous range and complexity of issues facing our nation," Brock said, citing Dole's "recognized mastery of moving a program through an increasingly independent Congress."

Brock said that perhaps his greatest satisfaction in the labor job came from knowing that 6 million more Americans had jobs today than when he took over in 1985.

A former Republican national chairman, Brock became labor secretary after the indictment of Reagan's first labor chief, Raymond J. Donovan, who was later acquitted. Brock is widely credited with rebuilding departmental morale and credibility with Congress.

Horner, if nominated by Reagan and confirmed by the Senate, will take over a 17,487-employe department with a heavy agenda on Capitol Hill.

Among pending labor matters are efforts to require a 60-day notice before plant closings or massive layoffs, a bill to increase the minimum wage from $3.35 to $4.10 an hour, and a measure to force employers to notify workers of possible hazards to which they may have been exposed. The administration opposes all three.

At the same time, Brock has pushed hard for two major proposals of his own: a $1 billion bill to help dislocated workers and a major pension reform bill.

Although Horner is not widely known within the labor movement, she has been a loyal Reagan lieutenant as director of the Office of Personnel Management. She has pushed through a pet Reagan project to test federal employes for drug use and has tried unsuccessfully to win passage of a bill to simplify civil service rules.

She took over at OPM in 1985, succeeding the contentious Donald J. Devine, who was unable to win confirmation to a second term. Civil servants found her goals were much the same as Devine's and included more merit pay for employes and cutting the government's high pension costs, but she raised fewer hackles in pursuing them.

Nevertheless, she made few friends among federal union leaders. "I can't believe that {the president} puts so little importance on labor that he would seriously consider putting in a lightweight with no background who has no sensitivity to the needs of workers or the needs of unions," said Kenneth T. Blaylock, national president of the American Federation of Government Employes, the largest federal union.

Robert Tobias, president of the National Treasury Employes Union, the second-largest federal union, called her a "poor choice" who has "done nothing to foster cooperative efforts between unions and management."

In announcing his resignation yesterday, Brock became the second member of the Reagan Cabinet to resign to work in the Dole campaign. The candidate's wife, Elizabeth Hanford Dole, resigned as transportation secretary Oct. 1 to work full time in his behalf. Her resignation left Reagan with no women in his Cabinet.

Horner worked for George Bush in the 1980 presidential campaign.