RICHMOND, DEC. 4 -- A federal appeals court judge said here today that Caleb Daniel Hughes, charged with last year's abduction of 5-year-old Melissa Brannen, probably would have to seek a fair trial outside Fairfax County if the court revealed the full content of an FBI affidavit in the case.

If the news media published the small section of the affidavit that has been withheld by a judge, "I don't think there's any doubt" Hughes would have a difficult time receiving a fair trial in Fairfax, said Judge Hiram E. Widener Jr.

A three-member panel of the 4th U.S. Circuit Court of Appeals heard arguments today from The Washington Post, Hughes's defense attorney and two prosecutors on whether the entire document should be made available to the public. The panel did not rule and gave little clue as to the content of the section under dispute.

Peter D. Greenspun, Hughes's attorney, distributed copies of the complete affidavit to the judges and described the passage at issue as containing "an overwhelmingly specific piece of information that is inadmissible at trial and would absolutely prejudice a jury."

Assistant U.S. Attorney William G. Otis said "the information it reveals is so specific and so unappetizing that it might well lead the reader to an unshakable belief not particularly to Hughes's advantage."

But Otis added that it would not be "impossible or extraordinarily difficult for Hughes to receive a fair trial even assuming the paragraph is unnsealed." He said recent cases involving former national security official Oliver L. North, D.C. Mayor Marion Barry and political extremist Lyndon H. LaRouche Jr. show that impartial jurors can be found even in heavily publicized cases.

Hughes was indicted Nov. 19 on charges of abduction with intent to defile, a felony carrying a possible prison term of 20 years to life. Witnesses said they saw Melissa Brannen talking with Hughes during a neighborhood Christmas party at a recreation center at an apartment complex where Hughes worked.

The trial is scheduled to begin Jan. 28 in Fairfax Circuit Court.

Last week, The Post asked that the affidavit be unsealed, arguing that because Hughes already had been indicted such a disclosure would no longer compromise the investigation of Melissa's disappearance.

Despite objections from Greenspun, all but one paragraph of the affidavit was made available. U.S. District Judge Albert V. Bryan Jr. allowed the paragraph to remain restricted while Greenspun appealed the case to the 4th Circuit.

Kevin T. Baine, an attorney for The Post, said today that Hughes could receive a fair trial even if the material were released and generated publicity. He noted that Judge Bryan had said last week that courts in Alexandria had experienced little problem in choosing impartial juries, even in a case in which a man was convicted of pretending to have abducted Melissa Brannen and extorting money from her family.

Greenspun and Fairfax Assistant Commonwealth's Attorney Stephen A. Best, in a rare show of unity between defense and prosecution, asked today that if the appellate panel orders release of the passage that it wait until the completion of Hughes's trial.