One of the 12 defendants charged in the beating death of Catherine L. Fuller was overheard saying Fuller was killed in a Northeast Washington alley during a robbery attempt because she recognized one of her assailants, a prosecutor alleged in court yesterday.

Assistant U.S. Attorney Jerry S. Goren said the government planned to introduce at the trial a statement from a witness who heard Timothy Catlett say "we had to kill her because she recognized" someone.

Goren's motion to introduce the alleged Catlett statement came during the third day of pretrial motions in the case before a D.C. Superior Court judge.

Several other statements allegedly made by the defendants and overheard by others also were introduced yesterday, and graphic photographs of Fuller's battered body were offered as evidence.

Some of the 12 defendants, a number of whom are teen-agers, stretched to see the photographs as Goren and Jeffrey Behm, another prosecutor in the case, held them aloft; other defendants bowed their heads and turned away. There were gasps from onlookers.

"These pictures are absolutely disgusting," said defense attorney Michele Roberts, whose objections to admitting as evidence some of the large photographs were shared by the other defense lawyers. "What they will do is make the jury disgusted."

Judge Robert M. Scott agreed that some large black-and-white photographs and some smaller color ones showing a lot of blood were "inflammatory" and should not be admitted, but he said the others showed the "facts" as they were. "We all know this was a pretty tough thing," Scott said.

Fuller's battered and lacerated body was found last October in a glass-strewn garage in an alley behind the 800 block of Ninth Street NE, near Fuller's home. Police allege Fuller was followed as she walked home and then dragged into an alley as the defendants attempted to rob her, repeatedly beating and kicking Fuller as she struggled.

Police allege that Fuller's nearly naked body was dragged over the glass into the garage where the beatings continued and a pole-like object was thrust into Fuller's rectum while some of her assailants cheered. All 12 defendants have been charged with first-degree murder, kidnaping and robbery.

Over the objections of Catlett's attorney Frederick Sullivan, Scott admitted conditionally the statement in which Catlett is alleged to have been overheard discussing why Fuller was killed.

Goren said yesterday he also planned to introduce a letter the prosecutor said was written by one of the defendants.

"You never ask me did I do it," Goren quoted a letter allegedly written by Levy Rouse and intercepted by the government. "Well, here it goes? I dragged the lady in the back the garge sic whille sic everyone else did what they did."

Rouse's lawyer, Lillian McEwan, denied Rouse wrote the letter. Scott said he planned to admit the letter, assuming it was written by Rouse, and reserved a final decision pending results of a handwriting analysis. Goren did not say to whom the letter was addressed or how the government had intercepted it.