Levy Rouse, one of 10 young persons on trial in the beating death of Catherine L. Fuller, denied prosecution allegations yesterday that he was a man so violent he had threatened his pregnant girlfriend, telling her that he "did the worse possible thing to that lady in the alley."

But later during cross-examination, Rouse told a D.C. Superior Court jury that at one time he had threatened to "blow up" the house of codefendant Russell L. Overton after Overton accused him of being a "police snitch" in another case.

Rouse, 20, whom witnesses have identified as the person who thrust a foot-long pole into Fuller's rectum, said in his second day of defense testimony that he believed the people responsible for Fuller's death should "pay the price."

"Whoever done it needed to pay for it. It's as simple as that," said Rouse, denying prosecution allegations that he was "unusually interested" in the investigation of Fuller's death.

Rouse, who said he did not arrive at the alley until Fuller's body was being removed, told the jurors that as he watched he thought about his sister, who was badly beaten and thrown in a trash can three years ago.

"I just said to myself someone's sister is dead," Rouse testified.

Later in the day, the third defendant to take the witness stand, Kelvin D. Smith, 20, 1007 Fourth St. NE, also denied being in the Northeast alley or abandoned garage where prosecutors allege Fuller was beaten to death during a robbery over a coin purse, adding that he "couldn't believe something like that happened in that area."

Attorneys for Felicia Ruffin, 17, the only female charged in the case, rested her defense yesterday without presenting any witnesses.

After Rouse's testimony and that of Smith and his witnesses, some defense lawyers said they believed neither man's alibi held up well under cross-examination by Assistant U.S. Attorneys Jerry S. Goren and Jeffrey Behm.

Their comments seemed to widen the rift that developed among defense attorneys Friday when some argued for separate trials, charging that Rouse's alibi was so "incredible" it would contaminate the defenses of the other nine on trial.

When one of Smith's witnesses completed her testimony yesterday, one attorney said, "Jerry just got himself another witness."

The girl, 15-year-old Renee L. Walker, testified she talked on the telephone with Smith repeatedly on the afternoon of Fuller's slaying. But during cross-examination, she became confused about dates and when questioned about discrepancies with her testimony to a grand jury, denied she had ever made such statements.

In an unusual effort to show that her client had not fabricated his alibi, Smith's lawyer Greta Van Susteren had him leave the courtroom during the testimony of his grandmother, 55-year-old Carrie Anderson, who said Smith was home in bed and on the telephone the afternoon of Oct. 1, 1984, when Fuller was killed.

When Smith returned to the courtroom, he told jurors that another defendant, Christopher Turner, 19, was with him at his grandmother's house. But some of Smith's descriptions of his activities that day contradicted his grandmother's.

Smith's attempt to establish an alibi for the day of Fuller's death was a change from the defense his attorney had told Judge Robert M. Scott that she might pursue. Van Susteren told Scott out of the presence of the jury that she was considering placing Smith in the alley as an innocent bystander.

Other defense lawyers, who said they had privately urged their clients to put on an "innocent presence" defense, said the presentation of Smith's defense highlighted the difficulty of trying to establish an alibi.

In their testimony, both Rouse and Smith said they knew most of the other defendants -- describing some as best friends -- and that the group spent time together in the neighborhood park where prosecutors say the plot to rob Fuller was conceived.

Their testimony also gave a glimpse into lives led by some of the defendants.

Rouse said yesterday he learned to read in jail after he was arrested and described his employment history as one of a job for a month here or two months there. He said he was the father of two children by two women.

Smith said he had dropped out of school after ninth grade and usually did not rise until 4 p.m. Smith said he is the father of one child and had many girlfriends, but denied fathering a child of a prosecution eyewitness who identified him as beating Fuller.