Rep. Louis Stokes (D-Ohio), chairman of the House ethics committee, was convicted by a Montgomery County jury last night of driving while under the influence of alcohol but acquitted of a more serious charge of driving while intoxicated.

The Circuit Court jury, which deliberated 6 1/2 hours, also convicted the 58-year-old congressman of running a red light.

Stokes told reporters: "Obviously I am quite disappointed . . . Consequently, I have informed my attorney to take such legal action as is necessary for my vindication." He refused further comment.

Defense attorney R. Kenneth Mundy called the outcome "a gross disappointment, very disconcerting" and said, "it is our intention to pursue the matter in all appropriate means and through all appropriate channels." Mundy, who also said it has not been decided whether to appeal the verdict, would not elaborate.

The charges resulted from an incident at 2:15 a.m. last March 25 when county police stopped Stokes in Wheaton after he drove the wrong way on Randolph Road and went through a red light. Stokes maintained he was not intoxicated but was tired, hungry and suffering from an allergy at the time of his arrest.

Driving under the influence is punishable by up to a two-month jail term and a $500 fine, but prosecutors have said they will not seek a jail sentence. The maximum sentence for going through a red light is a $500 fine. Driving while intoxicated, of which Stokes was acquitted, carries a maximum penalty of a year in jail and a $1,000 fine.

No date for sentencing was set last night.

Jury foreman Milfred Brown, an aeronautical engineer who lives in Bethesda, said the jurors concluded that Stokes' driving "was not a major problem," but that certain factors persuaded them that alcohol had "affected his judgment and discretion to the extent that normal coordination was affected and his physical and mental powers were diminished."

At one point in their deliberations, the jurors asked to have the judge's instructions regarding driving under the influence repeated. A guilty finding on the more serious driving while intoxicated charge would have required a conclusion that driving ability was more seriously impaired.

Brown said factors that influenced the verdict were testimony about "the possibility that Stokes had alcohol on an empty stomach"--Stokes maintained he had had only two glasses of white wine--police testimony that there was an "odor of alcohol" on Stokes' breath and the congressman's "confusion in not passing a portion of the sobriety tests" that police gave him on the street.

Commenting on county police performance in the widely publicized case, Brown said jurors felt they "did what they should have done, but they could have done it better."

Asked whether the jurors believed Stokes testimony about the two drinks, Brown said, "There was no way to judge whether he had two or more."

The jurors began their deliberations yesterday at the close of a four-day trial after hearing Stokes' attorney argue that police had tried to humiliate the congressman and a prosecutor say that Stokes' defense required too many "leaps of faith" to be believed.

In closing arguments, defense attorney Mundy told the jurors they should not trust the testimony of county police because the officers had decided in advance that Stokes was drunk.

Mundy said Officer Henri DeSibour III had decided that Stokes was drunk "from the moment he stopped him to arrest him." The police "just went through a ceremonial dance" of "meaningless" sobriety tests after Stokes was stopped and were "playing games and were trying to humiliate him out there," Mundy said.

Mundy also cited a statement police issued soon after the arrest that said Stokes had claimed congressional immunity from arrest. Mundy noted that police had retracted that statement, which he called "a vicious and offensive lie."

Prosecutor Robert Greenberg said the congressman's defense required too many "leaps of faith." If jurors believe Stokes' testimony that he had only two glasses of wine before his arrest, Greenberg said, then Stokes could not have been intoxicated. But Greenberg noted that Stokes had told reporters on April 13 that he had nothing to drink on the night in question.

Stokes testified last week that he had had one glass of white wine in his Capitol Hill office shortly after midnight and a second at the nearby Hyatt Regency Hotel. A hotel bartender, Barbara Kachur, testified he had just one glass of wine at the bar and that he appeared sober when he left three-quarters-of-an-hour before his arrest.

The roadside sobriety tests given Stokes consisted of alphabet recitation, walking a straight line and touching the tip of his nose with his fingers. Officer DeSibour testified the congressman failed all three, but Stokes testified he believed that he had passed. No chemical tests of Stokes' blood alcohol level were undertaken.

Stokes was not charged until three weeks after the incident because Montgomery police said that after consulting with U. S. Capitol Police they believed he had congressional immunity.

As the jurors deliberated yesterday afternoon Stokes waited outside the courtroom chatting with his staff and family, including hus brother Carl, former mayor of Cleveland.

Maryland's Motor Vehicle Administration is empowered to suspend the driver's license of someone convicted of driving under the influence. But prosecutors noted that Stokes has an Ohio license and said they don't know whether Maryland and Ohio have a reciprocity arrangement that could resuult in the suspension of his license.

Last April, D.C. Del. Walter E. Fauntroy publicly accused Montgomery County police of charging Stokes because he is black. There "appears to be a pattern developing against black leaders" across the country, Fauntroy said.

No mention of race was made at the trial, and both Mundy and Thomas Heeney, the second defense attorney, said they did not consider race a factor either in the arrest or the prosecution of Stokes.