A police union went to federal court to challenge a new department policy to administer chemical breath tests, similar to those used in drunken-driving stops, to any officers who kill or wound someone.

Patrolmen's Benevolent Association President Patrick Lynch said yesterday that the 24,000- member union would challenge the sobriety tests on constitutional grounds, arguing they violate protections against unreasonable searches. "There is no reason or justification to subject an officer who legally fires a weapon ... to the humiliation and psychological trauma of a mandatory Breathalyzer test," Lynch said in a statement.

In response, Police Commissioner Ray Kelly said he was standing by a policy which, according to written order, is meant "to ensure the highest levels of integrity at the scene of firearms discharges."

Kelly announced in June that he would adopt the breath-test measure based on police recommendations to study its undercover operations, amid community outrage over the police shooting of Sean Bell.

Bell, 23, was killed and two friends were wounded in a 50-bullet barrage after his bachelor party at a Queens topless bar in November 2006. Some of the undercover officers had been allowed by the department to consume up to two drinks at the bar to preserve their cover.