Federal Trade Commission Chairman Michael Pertschuk told Congress yesterday the agency may in the future seek new legislation giving the antitrust enforcement agencies explicit authority to challenge conglomerate mergers.

There has been a continuing debate in academic and legal circles about whether the mergers - between companies that are essentially unrelated, like the recent Mobil-Marcor merger - are in the the public interest since they contribute to an increasing concentration of economic power in the hands of fewer and fewer corporations even though they may not violate the antitrust laws in the traditional sense.

The laws currently bar mergers between firms where the combination may substantially lessen competition or tend to create a monopoly.

Last month, Attorney General Griffin B. Bell, whose antitrust division shares enforcement of the antitrust laws with the FTC, suggested that very large cases which seek to break up monopolies held by a single firm or a few firms may be too big for the courts. As alternatives, he suggested that very large cases might be brought in Congress as legislative matters, that Congress could pass legislation outlying guidelines for reorganizing concentrated industries, or that a rule-making approach could be utilized.

The hearings which began yesterday are the first of a general oversight nature on antitrust enforcement in decades and mark Sen. Edward M. Kennedy's first venture into the field as the subcommittee's new chairman. In opening remarks, he questioned whether the laws themselves, the enforcing agencies and their procedures, and the courts are adequate to do the job the Congress intended when it passed the antitrust laws.

In other testimony, three federal judges testified that the courts are able to handle the large complex antitrust cases despite the increasing doubts that are being raised but they all had suggestions about how the situation could be improved:

United States District Court Judge William J. Campbell of Chicago suggested that the grand jury in antitrust criminal prosecutions is a primary cause of delay and should be abolished. Although elimination of grand juries would take a constitutional amendment generally, he said they could be eliminated in antitrust matters if antitrust crimes were reduced from felonies to misdemeanors.

Judge Campbell also suggested that the antitrust division be given more funds to hire lawyers from the private sector in important cases. Although he said he was impressed that the division was able to procure "such excellent service at the salaries it is able to pay," he said "in the main . . . as an overall observation it is my considered opinion that the ability of these fine lawyers is slightly below that which the average large corporation defendant is able to employ on behalf of the defense."

Judge William Campbell, of Kansas City, Mo., cited numerous antitrust cases which were tried in a relatively short time and suggested "the key is for the judge to take judicial control of the case." Rampant delays and extended periods of "discovery" were lawyers seek materials from the other side "can't occur unless the judge is a party to it."