SEATTLE, DEC. 9 -- A woman was arrested today on charges she killed her husband and a woman by contaminating Extra-Strength Excedrin capsules with cyanide, tamperings that led to a nationwide recall and to tougher packaging requirements for over-the-counter drugs.

Stella Nickell, 44, was arrested at her home in Auburn, south of Seattle, by FBI agents and police, but officials would not say what may have motivated the alleged tampering in 1986 or what finally caused them to arrest Nickell, who was reported to be the prime suspect in the case seven months ago.

Nickell apppeared before a federal magistrate and will remain in custody pending a detention hearing on Friday.

Following an 18-month investigation, a federal grand jury indicted Nickell on charges of causing the June 1986 deaths of her husband, Bruce Nickell, 52, and Sue Snow, 40, and of putting cyanide in Extra-Strength Excedrin found on store shelves.

Nickell died six days before Snow, but it was not known he was poisoned until after reports of Snow's death. At that time, Stella Nickell told authorities her husband suffered symptoms similar to Snow's and turned in two bottles of Excedrin capsules from the family medicine cabinet, both with cyanide.

It is believed the indictment marks the first time anyone has been charged with direct involvement in tampering deaths dating back to seven fatalities from cyanide-contaminated Tylenol in 1982 in Chicago.

Auburn Police Chief Jake Evans refused comment on a possible motive or what led to Nickell's arrest, saying that he feared prejudicial news coverage about the incident would lead to a change of venue.

Evans said that although Nickell was arrested on federal charges that does not preclude the state from bringing murder charges against her.