Frank L. Rizzo said yesterday that he wants a third term as mayor of Philadelphia and will press for a change in the city charter to make it legal for him to run.

He said he would "campaign day and night to . . . reform the city charter so that Frank Rizzo can have the opportunity to run again for mayor."

At present, Philadelphia's charter prevents a mayor from serving more than two successive terms. The amendment abolishing that provision will be voted on Nov. 7. The next may-oral election is one year later.

Organizations on both sides of the question have already begun building forces and war chests. Immediately following Rizzo's City Hall press conference, City Commissioner Eugene E. J. Maier, a longtime Rizzo foe, announced te formation of a group to block the mayor's desire.

Maier said Rizzo has "a record of deception, of mismanagemet and of political favoritism."

Domocrat Rizzo, 57, first won election in 1971 after resigning earlier that year as police commissioner. Three years ago he trounced two opponents to win a second term. His margin of victory was more than the vote total of the Republican and Independent candidates combined.

He survived a failed polygraph test on political deals in 1973 and a 1976 recall effort that was killed by the Pennsylvania Supreme Court.

Six months ago he announced he would not seek a charter change and another term. Since then the city has experienced an eight-day municipal workers' strike, a shootout with a controversial organization called MOVE, and a weeklong teachers' strike.

Latest published polls show that voters here oppose the charter change by almost two to one. And if the charter were amended, the Philadelphia Daily News poll said. Rizzo would lose by an even greater margin.

That poll and others have left Rizzo undeterred.

"You start polling after today," he said as he announced his candidacy.

Rizzo's relations with the black community promise to be a factor in the charter campaign.

Before a German-American audience last week, he was introduced as the "last white hope." In his prepared statement yesterday, he repeated his opposition to: public housing in neighborhoods where residents don't want it, affirmative action quotas, and school busing.

"There is no question where I stand," he said.