Eugene J. Banks, an 18-year-old District of Columbia man who shot a cab driver in the back of the head last January, was convicted of second-degree murder yesterday by a Prince George's County jury.

However, the jury acquitted Banks of two other charges that carried a possible death sentence - first-degree murder and felony murder. Defense and prosecution attorneys said after the verdict that Banks may have beaten those charges because of the jury's fear that he could become the first victim of Maryland's new capital punishment law.

"In my mind," said the prosecutor, Assistant State's Attorney Michael P. Whalen, "the verdict reflected their thoughts to try to avoid the death penalty." Defense Attorney Fred Warren Bennett said the death penalty "at the very least was in the back of their minds."

Jury foreman Larry Roelofs would not comment on the verdict, saying only that "the jury voted unanimously not to talk about our deliberations."

Banks was the second man to be tried in Maryland on charges that could have resulted in the use of the state's year-old capital punishment law. Last May, the first man to be tried under the law, William Joseph Parker, escaped the death penalty because of an ambiguity in the statute.

Yesterday's verdict, which came after nearly four hours of deliberation by the jury, was considered a victory by defense attorney Bennett, who had told the jury that the shooting was a second-degree murder because Banks shot the cab driver in a state of panic, without premeditation.

A first-degree murder must be "premeditated, willful and deliberate," while second-degree murder is intentional but not premeditated.

"I'm elated," said Bennett. "The second-degree murder charge showed that the killing wasn't an accident but that it was done on impulse or out of panic."

Prosecutor Whalen, who sat quietly as the jury returned its verdict, said he was "crushed." "There was no evidence of fear or panic either during or after the incident," he said.

Banks and an accomplice were accused of robbing and murdering the cab driver, 37-year-old Robert Andrew McNeil of Washington, last Jan. 20. The accomplice, 25-year-old Raymond White, is being tried separately.

The second-degree murder conviction carries a maximum sentence of 30 years in prison. Banks was also convicted of armed robbery, false imprisonment and two handgun violations for which he could receive a total sentence of 55 years.

Banks and White have also been charged with robbing and murdering another Washington cab driver, Flora Washington, only 12 hours before the McNeil murder. Prosecutors are seeking the death penalty for Banks in that case, which has yet to come to trial.

Although he remained calm and expressionless throughout most of yesterday's proceedings, Banks appeared to be crying after the verdict was read. The courtroom audience let out a gasp when the jury foreman read "not guilty" to the charges of first-degree and felony murder.