A former CIA explosives expert and three Cuban exiles will soon be sought by federal authorities for questioning in the investigation of last year's Embassy Row bomb-murder of former Chilean Ambassador Orlando Letelier, according to informed sources.

Edwin P. Wilson, the former Central Intelligence Agency operative, and the three Miami-based Cuban exiles came to the attention of federal officials when they learned that Wilson was under FBI investigation in an unrelated assassination plot abroad.

Wilson allegedly sought to recruit the three Cubans to kill a political opponent of the Libyan leader, Col. Muammar Qaddafi, last year, according to the sources.

Wilson heads a small consulting firm here called Consultants International. It is involved in the arms export business, Wilson was out of the country yesterday and could not be reached for comment.

In reviewing information developed in the Libyan investigation of Wilson, investigators have established these possible connections with the Letelier case:

Wilson had a secret contract with the Libyan government to provide detonation devices called "timing pencils" - a tube filled with chemicals that can be remotely controlled to trigger explosions. Such a "timing pencil" is believed to have been used to detonate the bomb that exploded beneath Letelier's car.

The three Cuban exiles arrived in the Washington area just three days before the Sept. 21, 1976, bombing of Letelier's car.

One of the Cuban exiles, an explosives expert believed to have been trained by the CIA in the 1960s, met in Miami recently with a close associate of other Cuban exiles who have been chief suspects in the Letelier case.

Assistant U.S. Attorney Eugene M. Propper, who is in charge of the Letelier investigation, met with CIA officials last week and asked for all files and information on Wilson and the three Cubans, the sources said.

The three Cubans are not among the 10 anti-Castro Cubans who have reportedly been questioned already by the grand jury investigating the Letelier murder.

"These are new Cubans and a completely new direction for the case," said one source familiar with the investigation. The sources said, however, that the extent of Wilson's involvement, if any, could not be learned until Wilson is questioned.

In the Libyan investigation, the sources said that Justice Department attorneys are not sure if any U.S. law has been violated because the department has no jurisdiction to prosecute crimes committed abroad.

The Libyan case is now in the Justice Department Criminal Division for review.

That investigation began last year when CIA officials learned that a former employee was allegedly recruiting Cubans for terrorist activity.

According to the sources, Wilson was acting under a contract with the Libyan government and wanted the Cubans to assassinate a Libyan who had exiled himself to Egypt much like Letelier had driled himself to the United States after the September, 1973, coup in Chile and a year of imprisonment there.

The Cubans turned down the job offer, which was made by Wilson at a meeting in Geneva, Switzerland, according to the sources.

Upon learning of this, the CIA requested the FBI open an investigation of Wilson. This case was so sensitive that President Ford was personally informed of it.

Wilson's contract with Libya included a promise to supply thousands of timing pencils. "It is one of the most alarming things I've ever seen," one source said. "There were enough [timing pencils] contracted for to support terrorist activity for the rest of the century."

The Libyan government has in the past supported terrorist activity. At a news conference last July 19, President Ford said, "We do know that the Libyan government has in many ways done certain things that might have stimulated terrorist activity."

In addition, the sources said that there is some evidence that Wilson may have had contact with one or more current CIA employees who have access to supplies of timing pencils.

It is not clear from the investigation how many, if any, timing pencils Wilson actually supplied to the Libyan government.

The sources said Wilson also tried to recruit other former CIA employees to be explosives instructors in Libya.

One former CIA employee was offered $100,000 a year but turned it down. Wilson himself had contracts valued at hundreds of thousands of dollars with Libya, according to the sources.

Wilson has declined to answer questions from FBI agents in the Libyan investigation, the sources said.

Consultants International is located at 1425 K St. NW. An official there said yesterday that the firm was not involved in any questionable activity.

According to the firm's own promotional literature, Consultants International could supply an army with equipment including patrol boats, parachutes, airborne accessories and armor-protected vehicles.

"Armaments can be arranged to meet the requirements of the purchaser," the literature says.

Sources said that Wilson had a contract with Libya to clear land mines but the contract was the "cover" for the real purpose of supplying detonation devices.

"Explosive detection devices" are one of the items on the firm's sales list.

Wilson's firm has received numerous licenses from the State Department Office of Munitions Control to export arms related material though no license has been granted to export any thing to Libya, according to government records.

Letelier, 44, former Chilean ambassador to the United States, was foreign minister and minister of defense in the government of the late Chilean Socialist President Salvador Allende.

At the time of his death, Letelier headed a foreign affairs research program at the Institute for Policy Studies in Washington. A staff member of the Institute, Ronni K. Moffitt, also died in the explosion. Her husband, Michael, a research associate, survived the blast.