Former vice mayor James P. Moran formally entered Alexandria's May 7 mayoral race yesterday, challenging his one-time mentor and five-term Democratic Mayor Charles E. Beatley to three debates.

Beatley, who is vacationing in California, could not be reached for comment yesterday but said last week that he would welcome Moran's opposition.

"In many ways, Mr. Beatley can take credit for fashioning this city into the kind of community that has attracted people such as myself into local politics," Moran said, acknowledging the former strong ties between the two. "But that is the past. Alexandria needs someone to lead them into the future."

Moran, a 39-year-old stockbroker, parted ways with Beatley, a 68-year-old retired airline pilot, when Beatley pushed for Moran's resignation last June after the latter pleaded no contest to a misdemeanor conflict-of-interest charge.

Moran recently called for Beatley to apologize for his public criticism of Public Safety Director Charles T. Strobel. Moran made the statement after a grand jury reported that Strobel was not guilty of wrongdoing. Moran said Beatley's refusal to apologize prompted him to challenge the mayor.

Forced to file as an independent because Beatley already had won the party's nomination, Moran said yesterday, "I'm a Democrat now and I'll always be a Democrat."

The only other mayoral candidate is John D. Williams, president of the Alexandria Taxpayers Alliance who also is running as an independent.

Several groups were scrambling yesterday to organize a debate after hearing of Moran's candidacy. "We'd like to hear the three candidates discuss the issues," said G. Barton Middleton of the Chamber of Commerce. "But we want it on our terms, not the politicians'."