Embroiled in a dispute with Montgomery County police over three traffic charges, Rep. Louis Stokes (D-Ohio) was emphatic: He would not hide behind congressional immunity, he said last week, because "I do not hold myself above the law."

But if the Ohio congressman was clear about his intentions, the legal concept of congressional immunity is anything but clear. And in the Washington area, whether a federal lawmaker gets charged when he violates the law appears to depend, in part, upon where he is caught.

The chief prosecutors in Fairfax and Arlington counties say that congressional immunity applies to certain offenses, including most traffic violations, if the member can prove that he was on his way to or from a session of Congress when the violation occurred.

However, law enforcement officials in the District of Columbia, Alexandria, and Montgomery and Prince George's counties assert that members of Congress are no different from other citizens when it comes to arrests.

Officials in all the area jurisdictions agree that for felonies, which are more serious crimes, congressional immunity never applies. Unlike diplomatic immunity, which gives top diplomats absolute protection from prosecution for all crimes, congressional immunity is ambiguous.

With 535 members of Congress living in the area, it's not uncommon for police to be faced with the dilemma of how to handle possible charges against a federal lawmaker.

Through the years, even as it has raised the public's ire, congressional immunity has shielded some lawmakers. One notable case involved former representative Joe D. Waggonner Jr. of Louisiana, who in 1976, according to police, "solicited" a D.C. policewoman assigned to a special vice detail in the 14th Street NW area.

Once police found out Waggonner was a congressman, he was quickly released on the grounds of congressional immunity. In the resulting furor, D.C. Police Chief Maurice J. Cullinane ordered a study of the policy based on U.S. Supreme Court decisions, and determined that lawmakers should be subject to arrest for all offenses just like anyone else.

The latest skirmish over immunity occurred in Montgomery County, where Stokes has been charged with three traffic violations, including one for driving while intoxicated. Stokes, who has denied the charges and plans to contest them in court, didn't raise the immunity issue. Still, police released him without charge after he was stopped on March 25 because they said they believed that, as a congressman, he was immune. Police later reversed their position, after their legal adviser said they had misinterpreted the complex immunity clause.

In Fairfax County, Commonwealth's Attorney Robert Horan believes the privilege applies to offenses, including drunken or reckless driving, that are not felonies. A lawmaker might be ticketed for such an offense, but if he were able to prove that he was on the way to or from a session when the violation occurred, then "that's a bar to prosecution," Horan said.

Horan said he could recall only two occasions in his 16 years in office when a member of Congress raised the immunity issue, both times in speeding cases. In one, Horan said, he believed the congressman was en route to work and he dropped the charge.

In the second case, the violation occurred at about 4 a.m. on a Saturday. "It was very, very obvious he was not on his way home from a session," Horan said, and by the time the matter came to court, the lawmaker relented.

Horan said he could not recall the name of the congressman in either case.

Arlington County Commonwealth's Attorney Henry Hudson said he has "never had a congressman or senator raise the immunity issue," but that if they were traveling to or from Capitol Hill on official business and the offense were not serious, immunity would apply. Hudson said the decision would be made "on a case-by-case basis."

The clause requiring all this unscrambling is Article 1, Section 6 of the U.S. Constitution, which states that representatives 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."

For nearly 120 years there apparently was little legal dispute over the clause, which often was used to protect colonial legislators from harassment in civil cases, according to Stan Brand, general counsel to the U.S. House of Representatives. Arrest in civil cases was common at the time.

The U.S. Supreme Court ruled on congressional immunity in 1908 in a case in which a congressman, convicted of perjury, argued that he was immune from imprisonment because being in jail would deprive him of his right to go to and from sessions of Congress.

The trial court overruled the congressman's objection, and later, the U.S. Supreme Court ruled that congressional immunity was never meant to apply to criminal cases or proceedings.

Since then, members have sought congressional immunity from arrest with varying degrees of success. Last September, Del. Walter Fauntroy, the District's nonvoting member of Congress, claimed congressional immunity when a policeman in North Carolina arrested him for taking part in a protest. Fauntroy recalled that the policeman replied, "I'm no constitutional lawyer," before spiriting him off to jail. The charges against Fauntroy and most of the other protesters were later dropped, and immunity never became an issue.

Still, the policeman is not alone in his quandary over the subject. Even students of the Constitution disagree.

Joseph DiGenova, principal assistant U.S. Attorney in the District, said he believes the 1908 Supreme Court decision "is very clear that this privilege does not apply in criminal cases. It's just incredible how blunt the opinion was" on this point.

Brand was equally adamant that there is "still an argument about what is a criminal matter." He said a state could attempt to define something as criminal to impede a member of Congress from getting to a session. In such a case, he said, he would argue that immunity applies.

The privilege has important force in civil cases.

For instance, if a congressman were subpoenaed as a witness in a lawsuit and did not appear because Congress was in session, a judge might find him in contempt of court and order him to jail. In that case, Brand argued, congressional immunity would prevent the lawmaker's incarceration.

The debate over immunity is not likely to end. "You've got to give some meaning to the constitutional provision," prosecutor Horan said. "Let's face it . . . . It's not as broad as diplomatic immunity, but it is an immunity, nonetheless."