Two sophisticated bombs, designed to detonate at the slightest touch, killed a stockbroker and the wife of his former business associate in separate explosions here today. Salt Lake City Police Chief Bud Willoughby said detectives suspect a "hired assassin" of planting the bombs, which were concealed in plainly wrapped cardboard boxes.

Killed were Steven F. Christensen, 31, of Centerville, and Kathleen W. Sheets, 50, of Salt Lake City. She was the wife of J. Gary Sheets, former president and chairman of the board of directors of the Salt Lake City-based CFS Financial Corp. Christensen served on the CFS board of directors until about three months ago.

Police late today were circulating a composite drawing of the man who may have delivered the deadly package to the downtown office building where Christensen worked. A task force of 40 detectives was formed to investigate.

Police are focusing on two likely motives: The first and most likely, they said, is that a disgruntled investor or businessman hired a killer.

CFS, a 12-year-old company that deals in real estate and financial planning, recently reported that its debts exceeded assets by more than $5.4 million. The company, which reportedly had 2,000 to 3,000 investors nationwide, indicated in a letter to clients that it was trying to devise a recovery plan.

"These are our suspects," said Salt Lake County Sheriff's Detective Capt. Bob Jack, waving an inch-thick computer printout of CFS investors.

Another possibility, according to police, is that the murders were ordered or carried out because of the controversial "white salamander" letter, which Christensen bought and recently turned over to the Church of Jesus Christ of Latter-day Saints. Sheets apparently helped finance research that established the letter's authenticity.

The letter, written in 1930 by Martin Harris, a close acquaintance of Mormon Church founder Joseph Smith, implies that Smith was practicing magic when he discovered the golden plates from which the Book of Mormon is said to have been translated.

The letter indicates that Smith told Harris the plates were protected by an old man who could transform himself into a white salamander -- a symbol frequently used in magic practices in that era.

Christensen died at 8:15 a.m., after arriving at his office on the sixth floor of the Judge Building. Police said he discovered a cardboard box wrapped in butcher paper lying near the door and bearing his name.

"He apparently reached down to pick it up," and it detonated, said John Tenney, a sixth-floor tenant who said he arrived moments after the explosion.

Mary Olpin, another witness, said she thought Christensen was carrying the package in his arms when it exploded.

Police said the bomb, a length of pipe filled with explosives, an electric detonator and cement nails, blew Christensen through his office door, which was torn off its hinges.

There were no other injuries in that explosion. The second blast occurred about 11:20 a.m. outside the Sheets home in an exclusive residential area near the city.

Salt Lake County Sheriff Pete Hayward said Mrs. Sheets was walking from her house when she apparently saw a package beside a wooden walkway near her garage. The plain package, with a newspaper on it, was addressed to Mr. Sheets and resembled the one delivered to Christensen, he said.

Hayward said the explosion occurred as Mrs. Sheets lifted the box, killing her instantly.

Chief Willoughby said the bombs were identical and showed a sophisticated knowledge of explosives. Sheriff Hayward estimated the force of the blasts to be equal to 1 1/2 to two sticks of dynamite.

"They were designed with one purpose in mind, to kill somebody," Willoughby said. "We don't have a mad bomber on the loose who wants to bomb the Salt Lake Valley . . . . These bombs were purposely set to purposly kill these individuals.''