Mayor Marion Barry skipped the D.C. State Democratic Party's annual Kennedys-King dinner last night to fly to Atlantic City to attend the World Boxing Association light heavyweight championship fight.

Barry, accompanied by two D.C. police bodyguards, planned to stay in Atlantic City overnight and return to Washington late today, according to Annette Samuels, the mayor's press secretary.

"The mayor rarely takes time out from work, and he likes fights," Samuels said in explaining why Barry decided to miss the biggest local Democratic Party event of the year.

About 350 Democrats, including members of the City Council and the mayor's staff, attended the $125-per-plate dinner at the Washington Hilton Hotel.

Rep. Morris K. Udall (D-Ariz.) told the crowd that President Reagan's imminent appointment of a new administrator for the Environmental Protection Agency will demonstrate whether he is committed to protecting the environment.

The congressman said Reagan had deviated from a history of bipartisan support for the environment that began when Theodore Roosevelt was president. Udall praised former president Nixon for appointing "good, solid conservationists to run EPA and the Interior Department," and called on Reagan to select someone with similar views to run EPA.