A state police corporal estimated today that Kevin N. Cooper's car was traveling 68.4 miles an hour when it struck an oncoming car head-on near Mount Airy, Md., killing five people, last Christmas Eve.

But the judge at Cooper's trial here on charges that include five counts of auto homicide while intoxicated hasn't decided whether the jury will hear Cpl. Al Liebno's calculations, which the defense calls "pure speculation and guesswork."

Carroll County Circuit Judge Donald Gilmore said he would rule Thursday on the admissibility of Liebno's estimates, which were made using measurements taken at the scene of the accident and which Liebno said have a 10 percent margin of error.

Liebno also estimated that Martha J. Proctor, the driver of the other car, was traveling 50.8 miles an hour at the time of impact, calculated with the same 10 percent error margin. Three of Proctor's grandchildren and two of her sons were killed in the accident.

In testimony that the jury heard today, Maryland's chief toxicologist estimated that the alcohol level of Cooper's blood would have been .14 at 3:50 p.m., the time of the accident, if he consumed the nine 12-ounce beers that a bartender has testified were served to him in the 3 1/2 hours before the accident.

Previous testimony has put the alcohol concentration of Cooper's blood at .12 at 5:15 p.m., when the first blood test was taken. Under Maryland law, a person with a reading of .13 is considered legally intoxicated.

Another state trooper testified that evidence showed that Cooper applied his brakes moments before the crash, leaving 15 feet of skid marks. He said there were no signs that Proctor braked. Proctor testified Monday that she speeded up and turned sharply to avoid a crash.