A rapt jury and an overflow courtroom crowd sat mesmerized yesterday by a black-and-white television screen as a trembling Paul Leon Jordan, captured on videotape, told of stabbing a 3-year-old child because she "saw what was what so I had to take care of it, too."

Jordan is accused of first-degree murder in the deaths Jan. 24 of the child, Crystin Fletcher, and her baby sitter, 56-year-old Cora Barnes, who, according to police testimony, was stabbed after a lovers' quarrel with Jordan in Barnes' Northwest Washington home.

Yesterday, in D.C. Superior Court, the prosecution played for the jury its key evidence, a hotly disputed videotape of Jordan confessing to the crimes -- a tape that the defense asserts shows a man debilitated by alcohol withdrawal, confessing to a crime he did not commit.

On the tape, a police sergeant asks Jordan, "How did you take care of" the child?

"With the butcher knife," Jordan replies.

As the tape played in the hushed courtroom, Jordan, hands neatly clasped in his lap, stared almost expressionless at his own image.

The tape showed Jordan sometimes offering halting answers, sometimes responding with long silences and sometimes shaking so violently that he could hardly grasp the cup of water he was trying to drink from.

In other parts of the nearly hour-long tape, Jordan, prodded by police questions, tells of making love with Barnes in the bedroom where the child was sleeping and then of having an argument with Barnes when the child's cries interrupted their lovemaking.

Later on the tape, Jordan says he got a butcher knife in the kitchen, and went back upstairs. "That's when I lost my head," Jordan says. "I started cutting on her Barnes ."

The tape and testimony yesterday by homicide Detective Joseph Schwartz, one of the two chief investigators in the killings, are the heart of the government's case in the slayings of Barnes and Crystin Fletcher, the only child of two District police officers.

Yesterday, Schwartz testified that before the videotaping, Jordan told him he often visited Barnes and brought candy for the child, whom he called "Little Sweetheart." Schwartz said Jordan confessed orally that he "choked" the child, then stabbed Barnes, then sexually assaulted the child.

Jordan also is charged with taking indecent liberties with a minor child and sodomy. He has pleaded not guilty to all of the charges.

As soon as prosecutor Amy S. Berman finished her questioning of Schwartz, the defense began its attempt to show, as outlined in its opening statement to jurors, that "Schwartz told Mr. Jordan lies and used special police psychological tactics to get Mr. Jordan to confess" during hours of interrogation Feb. 14.

Under cross-examination by defense attorney James H. McComas, Schwartz acknowledged that he lied to Jordan, by suggesting that police knew he had been in the Barnes home on a number of occasions, although Jordan insisted initially he had been to the house only once. Jordan, 48, of 1420 Clifton St. NW, had previously lived next door to Barnes, whose home was at 4321 Second St. NW.

"After 2 1/2 hours of questioning , Mr. Jordan told you he had been in the house only once," McComas said.

"Yes," Schwartz replied.

"But you didn't stop lying or using emotional pressure tactics until he confessed," McComas went on.

"Yes sir," Schwartz said. "That's one way to put it." Jordan eventually acknowledged visiting the house often, Schwartz said earlier in his testimony.

Schwartz also acknowledged that on the videotape Jordan made a number of statements about the killings that the detective knew were not true, including a statement that he took Barnes' body to the basement and that the child was wearing a dress the day of the slayings. Barnes's body was found upstairs in the house, and the child was wearing pants and a sweater, according to other testimony. Schwartz also acknowledged that he saw what McComas called "visible symptoms of illness" in Jordan during the videotaping, and that Jordan had been "tremulous and shaking" during questioning before that.

The defense has asserted that Jordan, an alcoholic, was suffering from withdrawal during the interrogation.

Schwartz acknowledged yesterday that he suspected alcohol withdrawal as the videotapiong was nearing an end, but that Jordan was not taken to D.C. General Hospital until five hours later.