A legal adviser to the Montgomery County police reversed course yesterday and said that Rep. Louis Stokes, the chairman of the House Ethics Committee, was not immune from arrest last Friday after he was stopped by police and failed three roadside sobriety tests.

Police said, however, that Stokes will not be charged because the officer at the scene failed to give the congressman a breath test, which is required by Maryland law before a drunk driving arrest can be made.

Stokes, in a statement released by his office yesterday, said that he did not claim constitutional immunity from arrest in the case, as the county police had previously reported, "nor was I under the influence of alcohol."

The county police yesterday agreed with the 58-year-old congressman that he did not request immunity and said the issue arose when the investigating officer realized Stokes was a congressman.

Bruce Sherman, an assistant county attorney who earlier this week agreed with a claim by the U.S. Capitol Police that Stokes was entitled to constitutional immunity from arrest in the case, said that further legal research "shows that a congressman is not privileged from arrest for drunk driving. A Montgomery County policeman could have either given him a citation or arrested him."

According to police, Stokes, a veteran Ohio Democrat, flunked three roadside sobriety tests after he was stopped by a county policeman at 2:15 a.m. last Friday, including recitation of the alphabet, walking a straight line and touching his finger to his nose.

But Montgomery police spokesman Cpl. Phillip Caswell said Stokes will not be charged because "the congressman was not afforded all of his constitutional rights at that time," such as being given a breath test as required by Maryland law.

Caswell said that since Stokes is now on a congressional trip to the Mideast and won't return until April 7, it would make no sense to charge him upon his return. "What purpose will it serve?" he asked.

Caswell said that an executive officer assumed that Stokes had claimed immunity and passed the story on to the police department's press office. The error was only discovered when the officer who stopped Stokes returned to work and gave his version of the incident, Caswell said.

Stokes, a former chairman of the Congressional Black Caucus, was spotted by a patrol car early last Friday driving down the wrong side of six-lane Randolph Road in Wheaton, police said. They alleged that he made an illegal U-turn, ran a red light and began to make another illegal turn onto Georgia Avenue.

"At that point the officer stopped him and detected the odor of alcohol," said Montgomery police Sgt. Harry Geehreng. "He was swaying and gave the impression of being under the influence."

Geehreng said the congressman then failed three routine roadside sobriety tests.

Caswell said yesterday Stokes showed the police officer his congressional identification and when the officer realized he was a congressman he took Stokes to the Wheaton police station. There, the officer, whom Caswell refused to identify, consulted with his shift supervisor and Capitol Police on how to handle the matter.

According to Caswell, Capitol Police advised that Stokes was immune from arrest under Article 1, Section 6 of the Constitution, which says that congressmen and senators "shall in all cases except treason, felony and breach of the peace, be privileged from arrest during their attendance at the session of their respective Houses, and in going to and returning from the same."

Sherman said that in a 1908 case, the Supreme Court ruled that breach of peace was meant to include all criminal cases.

Nonetheless, he said that the officer who stopped Stokes "acted in the utmost of good faith" in not charging the congressman because a state police handbook cites the constitutional arrest immunity clause for congressmen without any elaboration. Sherman said he is drafting a memorandum to Police Chief Bernard D. Crooke explaining the Supreme Court's interpretation of that clause.

In his statement, Stokes said he explained to police that he had worked at his office until 1:30 a.m. last Friday and "was extremely tired and exhausted" when he was stopped by police.

The statement did not mention any of the traffic violations police allege he committed, nor did it address police statements claiming that he flunked the three sobriety tests.

"The congressman's statement did not address that," Adrienne Gray, his spokeswoman, said. "All I can tell you is what is in the statement."