WASHINGTON - The U.S. Sentencing Commission voted unanimously yesterday to allow about 19,500 federal prison inmates, most of them black, to seek reductions in their crack-cocaine sentences.

The commission, which sets guidelines for federal prison sentences, decided to make retroactive its recent easing of recommended sentences for crack offenses.

Most of those eligible could receive no more than a two-year cut in their prison terms, but roughly 3,800 inmates could be released from prison within a year after the March 3 effective date of yesterday's decision. Federal judges will have the final say whether to reduce sentences.

The commissioners said the delay until March would give judges and prison officials time to deal with public safety and other issues.

The commission noted objections raised by the Bush administration, but said there is no basis to treat convicts who were sentenced before the guidelines were changed different from those who were sentenced after the changes.

The sentencing commission recently changed the guidelines to reduce the disparity in prison time for the two crimes. The new guidelines took effect Nov. 1.

U.S. District Judge William Sessions, of Vermont, a commission member, said the vote on retroactivity will have the "most dramatic impact on African-American families."

A failure to act "may be taken by some as particularly unjust," Sessions said before the vote.

More than 80 percent of federal defendants in crack cases are black. Most powder-cocaine convictions involve whites.

Even after the change, prison terms for crack cocaine still are two to five times longer on average than sentences for powder cocaine, the result of a 20-year-old decision by Congress to treat crack more harshly.

The commission said in 1995 that there was no evidence to support such disparate treatment.

Relatives of prison inmates applauded after the 7-0 vote. *