Mark Green, the director of Congress Watch, yesterday strongly criticized the performance of the Justice Department's antitrust division, saying it has failed to fulfill the promises laid down by its chief, John H. Shenefield, when he took office in 1977.

Addressing the Professional Association of the Antitrust Division, a group of Justice Department employees, Green said the division is filing fewer cases and avoiding tough issues, such as shared monopoly.

"These are people of intelligence, decency, independence and competence," Green said. "So why has so little changed?"

In a later interview, Green, who along with his associate Ralph Nader prepared an exhaustive study of the dividion during the early 1970s, said that during the last few years, division personnel have increased by 10 percent, although the division has filed about 20 percent fewer cases.

"It's hard to know why Shenefield failed to achieve the goals he announced when he began," Green said.

"Either there are or there aren't shared monopoly cases worthy of prosecution, but they've established a filter so fine that no case can get through it," Green told the group of lawyers and economists.

"The division can't go anywhere as long as law enforcers fail to pursue the ends they begin," Green said.

Green also criticized the division for failing to take the case for anti-trust enforcement to citizen groups other than business and legal representatives.

"Prosecutorial discretion frees you from political turmoil," Green said, noting the scandals that rocked the division in the Nixon administration years. "But ultimately the danger is that you lose your base of support."

Green urged the group to develop statistical data about the value of antitrust enforcement, so that consumer groups and others would have a greater understanding of the economic advantages of trustbusting.