President Reagan yesterday named Susan W. Liebeler, a controversial member of the International Trade Commission, as chairman of that quasi-judicial body, replacing Paula Stern, whose term expired.

Another Reagan appointee, Anne E. Brunsdale, was named vice chairman of the ITC, which investigates complaints of unfair trade practices brought by American industries that think they have suffered economic damage because of imports.

Liebeler also is under consideration for nomination by Reagan to the U.S. Court of Appeals for the Federal District, which hears appeals from decisions of federal agencies, including the ITC. She served on the Reagan administration transition team, but says she is a political independent, and holds a seat reserved for a Democrat or independent.

The ITC, once a sleepy government agency, has grown increasingly important as the United States has run four consecutive years of record trade deficits that are blamed by organized labor and industry executives for factory closings and job losses in American manufacturing. The commission's caseload increased 22 percent in 1985 over the previous year.

Both Liebeler and Brunsdale, the most recent Reagan appointee, have been accused by other commissioners and lawyers for domestic industries of basing decisions on their free-trade ideology instead of on the law.

The accusation was first made by Commissioner Alfred E. Ekes, a Republican and former chairman, in a footnote to an opinion. It was picked up by lawyers for domestic industries appearing before the ITC, and brought up at a House Ways and Means Committee trade hearing.

As a result, the House-passed trade bill would require Senate confirmations of the appointment of the ITC chairman and vice chairman. A similar provision is likely to be included by the Senate in any trade legislation it passes this year.

Lawyers representing importers, however, believe the criticism of Liebeler and Brunsdale is another sign of a growing protectionist sentiment in the wake of last year's $148.5 billion trade deficit.

Nonetheless, the two Reagan appointees have voted against petitions of unfair trade practices brought by domestic industries far more than the other four ITC members.

Liebeler ran into trouble on Capitol Hill when Reagan first nominated her to the commission in 1982, when Republican and Democratic members of the Senate Finance Committee questioned her interpretation of U.S. trade laws. In addition, Democrats argued that her position on the Reagan transition team disqualified her for an independent seat on the supposedly nonpolitical ITC.

Although the Senate failed to consider her confirmation the first time around, Liebeler was renominated by Reagan and joined the ITC in April 1984.

Stern, the outgoing chairman, is a Democrat who has been one of the most outspoken heads of the ITC. In speeches and congressional testimony, she has criticized the Reagan administration for its refusal to use, as a remedy for trade complaints, adjustment assistance for workers who lose jobs and communities that lose factories because of imports.

She also has suggested that the United States should auction quota rights instead of merely imposing import restrictions, and using the proceeds to make U.S. industries more competitive.