Two of the city's mayoral candidates have joined out-going Mayor Frank Rizzo in criticizing an unprecedented federal police brutality suit, but each has a different reason.

The Justice Department filed suit Monday alleging that Rizzo and other top city officials condoned widespread police brutality that was "arbitrary, unreasonable or shocking to the conscience," especially in contacts with blacks and Hispanics.

Rizzo, who is not eligible for reelection after his second term ends in January, told a news conference Monday that the suit was politically motivated, an attempt to appeal to minority voters who once supported President Carter.

The White House denied Rizzo's charge.

"Any implication that matters of this kind are political are incorrect," said White House news secretary Jody Powell in Washington, responding to a question at his regular news briefing.

Republican mayoral candidate David W. Marston, a former U.S. attorney, said the suit lumped "the vast majority of law-abiding police officers . . . with those who are guilty, and I believe that is wrong."

And William J. Green, the Democratic candidate for mayor, said he would preferred that the action had been delayed to give the next mayor a chance to institute changes in the department.

Others criticizing the suit included Police Commissioner Joseph O'Neill, who was named as a defendant, and Pat Stark, national president of the Fraternal Order of Police.

In Washington, Edward J. Kiernan, president of the International Union of Police Associations, said the union does not approve of brutality, but "We also do not condone unproven, reckless charges that depict the entire police force of committing brutality against the citizens of Philadelphia.

"Unless the charges are substantiated immediately, the situation will only inflame the tensions that already exist."

But Hilda Silverman, executive director of the American Civil Liberties Union in Philadelphia, supported the government, saying the suit "indicates a recognition of the magnitude of the problem and extent to which that problem has been created and sustained by the people at the top."

Alphonso Deal, who retired in November after spending 25 years as a Philadelphia policeman, said the suit was a "long time coming."

"I am so happy that they (the Justice Department) realize the real culprits are the mayor and the police commissioner and others at the top," said Deal, who now works full time for the National Association for the Advancement of Colored People.