John C. Marteny, the Falls Church man charged with murdering two women in their Vienna-area town house April 18, told police before he was arrested: "I killed them. I killed those girls," two police investigators testified in court yesterday.

The testimony came during a hearing in Fairfax County Circuit Court on a motion by Marteny's attorneys to suppress those and other statements he made to police during questioning May 1 at police headquarters. The hearing will continue Tuesday.

Marteny, 31, was charged with two counts of first-degree murder after more than six hours of questioning by police that included a polygraph examination, according to yesterday's testimony.

Investigators testified yesterday that Marteny was advised of his rights at least twice during the session and continued to answer questions. Marteny's attorneys contend that the questioning still violated his constitutional right to have an attorney present and not to incriminate himself.

Marteny, who said during a previous court appearance: "I'd just as soon skip the preliminaries," and "I'd just as soon take the electric chair right now," is charged in the strangulation slaying of Sandra Niccum, 22, and the beating death of Donna Tehan, 38, who were found dead in their town house April 20.

According to previous police testimony, Niccum was killed in a dispute with Marteny over cocaine and Tehan was killed when she walked in unexpectedly.

"There is ample evidence in this case that cocaine was in constant use in this house," Fairfax prosecutor Robert F. Horan Jr. said yesterday.

Marteny testified yesterday that at the time of the killings he had "a $300-a-day cocaine habit, and I had had it for the six months previous to the incident." He testified that before going to be questioned by police on May 1, he had taken one-eighth gram of cocaine, 1 1/2 Percodan sedative pills and 10 milligrams of the tranquilizer Valium.