Saying that the Fourth Amendment right to be safe from unreasonable search and seizure has been "severely distorted," the head of the Justice Department's criminal division yesterday testified in favor of a series of bills that would make it easier for prosecutors to use illegally obtained evidence in trials.

At issue is the "exclusionary rule" that provides that evidence obtained illegally--through improper wiretaps or unauthorized searches, for instance--may not be used in court against a defendant, even one there is reason to believe is guilty.

Three bills pending at the Senate Judiciary Committee would either limit or abolish application of the exclusionary rule in federal prosecutions and make it more difficult for criminals to be released on legal technicalities.

"I'm not saying that the exclusionary rule is a cause of crime," Lowell Jensen, assistant attorney general in charge of the criminal division, told the criminal law subcommittee. "But there are cases where clearly guilty defendants are acquitted and set free. I think any move we could make to restore the credibility of our system of justice . . . will have a positive effect."

Arguing against the legislation was Maryland Attorney General Stephen H. Sachs, a former federal prosecutor, who said the exclusionary rule is guaranteed by the Constitution and is beyond the reach of Congress.

"The rule is very fragile . . . . It appears to reward the undeserving criminal whom it sometimes frees because 'the constable blundered.' It seems to give aid and comfort only to the enemy in the war on crime. It makes almost no sense to citizens fed up with crime and impatient with legal technicalities who want to believe crime would disappear if only the courts stopped coddling criminals," he said.

But he added that very few criminals are actually let go by use of the exclusionary rule, while "it manifests our refusal to stoop to conquer, to convict lawbreakers by relying on official lawlessness, a vital demonstration to our commitment to the rule of law."

President Reagan has asked for changes in the exclusionary rule and the Attorney General's Task Force on Violent Crime last August asked that the rule be changed to allow the questionable evidence, as long as the police officer had a good-faith belief that he or she was conducting a lawful search.

One of the bills being considered would do just that, but Sachs argued that good-faith intentions don't help ordinary citizens when it comes to breaking the law. "There's certainly no good-faith exemption for violation of income tax laws," he said.

A second bill would abolish the exclusionary rule and allow victims of illegal searches and seizures to sue for civil damages. A third proposal is a combination of the two.

Jensen said the Justice Department favors the good-faith exemption, but said the department may have further recommendations.