A federal judge yesterday upheld the right of the National Organization for Women to use a convention boycott as a tool against states that have not ratified the Equal Rights Amendment. He called the boycott a legitimate political venture.

The case 'involves political opponents, not commercial competitors; and political objectives, not market-place goals," U.S. District Court Judge Elmo B Hunter said in his 30-page decision.

His action came 51 weeks after Missouri Attorney General John Ashcroft filed a suit charging that NOW's convention boycott tactics violated the Sherman Antitrust Act.

NOW officials maintain that the boycott has cost Kansas City more than $8 million in convention business and has cost St. Louis about $11 million. Similar boycotts in the other 14 states that have not ratified the ERA have resulted in millions of dollars in lost business, NOW says.

State officials contended that the boycott was "taking states as economic hostages with the ratification of the Equal Rights Amendment as the ransom."

Hunter disagreed, saying that the convention boycott "can be characterized as noncommercial in that its participants are not business interests and its purpose is not increased profits." And he said the boycott was not undertaken to advance the economic interests of the participants.