President Carter asked Congress yesterday to strengthen the collective bargaining rights of workers and impose stiff penalties on employers who violate the labor laws.

Outlining the President's congressional message on labor law overhaul, Labor Secretary Ray Marshall acknowledged that the proposals are controversial but said the administration intends to fight for them.

Marshall described the package - the result of intensive negotiations between the administration and the AFL-CIO over the last few weeks - as the "first comprehensive effort to reform our basic labor laws in 30 years" and predicted it will be "one of the major domestic accomplishments of the Carter administration."

Key elements of the package, which is expected to be introduced today by Sen. Harrisen Williams (D-N.J)., include:

Fixed deadlines for holding union representation elections, ranging from 15 to 73 days after authorization cards have been signed, in order to climinate delays that unions contend work against them.

Denial of federal contracts for three years to firms that "willfully and repeatedly" violate orders of the National Labor Relations Board unless the Labor Department finds that the denial would adversely affect the "national interest."

Compensation to workers for wage increases lost when employers unfairly refuse to bargain for a first contract, with workers to be paid the different between their existing wages and industry averages or some other relevant standard.

Double back pay to employees who are illegally discharged for union activities.

Expansion of the NLRB from five to seven members, broadening of its injunctive powers so it could bar firings of union activists; authority for two of its members (rather than the full board) to decide routine cases and more broad-scale rule-making by the board to avoid delays involved in case-by-case decisions.

Marshall said it is not "totally accurate" to call the legislation a "labor bill," asserting that businesses as well as unions will benefit from "reforms that will lead to a more smoothly functioning NLRB."

However, AFL-CIO President George Meany promptly endorsed the package and Richard Lesher, president of the U.S. Chamber of Commerce, denounced it as a "thinly veiled attempt to increase the size, financial strength and political power of organized labor by forcing unionization of the American worker . . ."

At his briefing, Marshall denied that the proposals would force workers to join unions, noting that they don't include organized labor's earlier proposal to repeal state right-to-work laws.