A federal judge yesterday refused to reduce the sentence of John Elbert Landon, the 30-year-old Maryland man sentenced to 10 years in prison for his role in the daring predawn break-in at the Lorton minimum security facility last May which left one inmate dead.

District Judge Albert V. Bryan Jr. denied a motion by Landon's attorney, Edwin C. Brown Jr., that Landon's sentence be cut, but granted a defense request that will permit Landon to be paroled at any time, rather than after serving one-third of his term.

Landon, who was convicted of assault and attempted murder, is serving his sentence at an undisclosed prison under the auspices of the Federal Witness Protection Program. As part of a plea bargain with prosecutors, he was sentenced last July, a month before his appearance in federal court in Alexandria as the chief prosecution witness against two men charged with killing Lorton inmate.

Landon's testimony helped convict Edward Ford, 32, of Alexandria and Germaine Stoddard, 24, of Northwest Washington on charges of murder and conspiracy to murder in the death of Douglas M. Boney, who was gunned down in what prosecutors said was revenge for the break-up of a Washington drug ring.

Prosecutor Karen P. Tandy yesterday reminded the judge of Landon's cooperation, but took no position on requests to reduce his sentence.