Add the respected antitrust firm of Bergson, Borkland, Margolis & Adler to the list of law firms hit hard by the Reagan administration's move to reduce government litigation.

The 40-lawyer firm, like others that specialized in antitrust or federal agency work, is hurting. A partner there confirms that up to a third of the firm's 24 partners, especially the junior partners, are looking for a new home and that five associates were told to be out by July 1. Several sources familiar with the situation say that more than half of the firm's 16 associates are looking for work.

Bergson, Borkland has been especially jolted by the cutback in antitrust work, several sources said, because the firm was late to diversify when the antitrust business dropped. And the areas it picked for expansion, environmental law and Food and Drug Administration law, are not exactly booming these days.

One partner said the firm simply was too big for the amount of business it anticipates getting in the next few years. He called the current changes "restructuring for the '80s."

No single piece of business, several sources said, has replaced the work generated by the Justice Department's antitrust suit against the three major television networks. Bergson, Borkland represented ABC during the eight-year fight and had from 12 to 15 lawyers employed full time on that case until it was settled in August 1980.

The firm made seven associates partners in late 1978, while that case was going strong, and since then has only elevated two associates to partnership. The last was Barry R. Goldsmith, who recently was named a partner.