The Senate Committee on Labor and Human Resources yesterday rejected President Reagan's nominee to become assistant secretary of labor for mine safety, and committee Chairman Edward M. Kennedy (D-Mass.) said the nomination will not go to the Senate floor.

The rejection occurred on a straight party-line vote, with nine Democrats opposing the nomination of Dorothy Strunk and seven Republicans voting in favor.

Democrats on the panel maintained that Strunk -- a senior legislative associate on the House Education and Labor Committee who specializes in occupational safety laws -- lacks the qualifications to head the Department of Labor's Mine Safety and Health Administration (MSHA), an agency of 2,800 employes charged with protecting the nation's miners.

The daughter of a coal miner, Strunk has worked on the House committee staff for 20 years.

Strunk was nominated to succeed David A. Zegeer, who retired from the Labor Department in January.

Labor Secretary William E. Brock had mounted a strong personal campaign for Strunk's confirmation, including an appearance before the committee last week. In a letter yesterday to Kennedy, Brock said if Strunk's nomination were rejected he would transfer the acting assistant secretary for mine safety, Alan C. McMillan, who is highly regarded by the committee, to another position.

The letter was interpreted as "a threat to let the agency flounder," acording to a Senate source.

The Department of Labor denied that interpretation, and in a statement released after the vote, Brock accused committee Democrats of engaging in partisanship at the expense of the nation's miners. He also said he would find another person for the president to nominate.

At her confirmation hearing last week, Strunk told the panel that her extensive experience working with the Mine Safety and Health Administration has prepared her to head the agency.

But the nominee's critics said the new assistant secretary would need technical expertise and management experience that Strunk lacks.

"This agency is in serious trouble. I really have serious doubts about whether she has the managerial ability needed for the job," Kennedy said, shortly before the vote.

The Labor Committee has criticized MSHA for lax enforcement of safety laws in a series of hearings over the past two years, and observers have said the agency is in turmoil.

The United Mine Workers and other unions opposed Strunk's nomination; the American Mining Congress, which represents mining companies, backed the nomination.