On Nov. 18, 1975, Farlan Speer, a shy, 42-year-old Stanford Ph.D. and former researcher at the National Academy of Sciences here, boarded Braniff Flight 15 at Dulles International Airport for a 3:20 p.m. flight to Oklahoma.

He has not been heard from since.

About the same time another man, calling himself Michael Carr Speer III - which was Farlan Speer's name until he legally changed it to Farlan Speer in 1973 - arrived in Oklahoma City with a briefcase full of references versity and the National Academy of Sciences.

This second man took out an Oklahoma driver's license, a loan, approached oil and utilities companies with investment opportunities and was hired by a multistate construction firm as a vice president.

All of this he did in the name of Michael Speer III.

The man who entered the Oklahoma business community with so much fanfare was 5 feet 9, with thick jet black hair and brown eyes. He had a swarthy complexion - "Indian" or "Spanish," according to those he contacted - and was missing the last joint on his middle finger and the tip of his ring finger on his left hand.

"It is always the same description," said Paul Speer, father of the missing researcher. "His description nowhere fits my son's," whom he described as 6 feet 2, blue-eyed, balding, and about 190 pounds.

On July 30, 1976, a private investigator retained by Speer's father interviewed the second man and a woman who claimed to be his wife, Dorothy Speer.

The investigator, Robert Cunningham, said he traced the license plates on the cars parked in front of the six-room surburban bungalow to a James D. Francis Sheker, a former Centreville man wanted by the FBI and Prince William County police on unrelated fraud charges.

Two hours after the interview, the investigator said, he returned to find that the couple had moved without leaving a forwarding address.

On Aug. 26, 1976, Cunningham said he received a collect telephone call from a woman identifying herself as Dorothy Skeker who said that she and her husband had taken false names - Michael and Dorothy Speer - to get a "new start in life."

Where is Farlan Speer, the reticent researcher with the genius IQ who could work a Sunday New York Times crossword puzzle in 10 minutes and speak several languages fluently?

"I asume he's dead," said his 74-year-old father, Paul Speer, a municipal finance consultant in Chicago. He said he has spent thousands of dollars on private investigators trying to find his son.

In mid-1975 Speer was employed as a researcher for the National Academy of Sciences in Washington, was winding up his work here and was soon to be uemployed.

His supervisor at NAS, Robert Long, described Speer as "trusting and naive . . . a little adrift on his own thoughts. He was better suited to being a quiet researcher than being thrown in with the sharks."

Speer placed a brief description of his background in a Labor Department bulletin in the hope of catching the attention of a prospective employer. Shortly thereafter he came across an employment ad for someone with just such qualifications in a newspaper, according to Washington police. Speer answered the ad and was contacted by a man claiming to represent an international mining company.

Details of the job could not be divulged he was told, because competing companies might discover the site of the mineral explorations, Speer told friends.

He would be making $50,000 tax free in the new job outside the U.S. and had received checks in the mail ranging from $200 to $500 while waiting for the job to start, Speer told friends.

"We thought Farlan was working for Howard Hughes," said Rashad Mills, a friend of Speer's.

Speer gave a man who identified himself as a representative of the mining company his resume, references, and several personal records when he applied for the job and in subsequent interviews.

"They wanted a total history of his background," said Faisal Klitzner, a friend of Speer's who overheard the interview. The mining company representative, Klitzner said, "wanted to know the guy's likes and dislikes, who he worked for, what school he want to from elementary school on, his friends, everything from soup to nuts." Speer also was told to get his passport in order, according to another friend.

The man who identified himself as the representative of the mining company was described as being about 5 feet 9, 160 pounds, with a complexion like that of a "Spaniard" or "Indian," according to several of Speer's friends. Speer's friends said they later identified that man from FBI photos as Sheker.

At the time Speer was attempting to get the mining job, Sheker was employed by Ames Associates, job placement service in Bethesda. Sheker had been working there for six months at a $30,000-a-year salary, according to Michael Ames, the business' owner.

Sheker was a "very private person, very tight-lipped," who claimed to have close ties with the CIA, Ames said.

[The CIA, in a Sept. 30, 1976, letter to Speer's father, said Skeker "has not ties with the agency."]

After Speer was chosen for the mining company job, he was told that he would have to go to Oklahoma City to be briefed on his job, then be flown to an undisclosed location for the actual mineral exploration.

"He was excited about his new job. It was an unknown, but it had a future," said Ruth Johoda, a friend of Speer's who drove him to the airport for his flight to Oklahoma City, and is the last person known to have seen Farlan Speer. Speer left his Fiat with a friend and planned to pick it up later, but never did.

Speer had recently been divorced, and had alimony payments to make, but police and investigators said Speer could have made those payments, that he had a sizable amount of money in his bank account when he left, and that his only outstanding bill was for $35 which he owned the gas company. Repeated efforts by The Post to reach Speer's estranged wife, who reportedly is living in California, were unsuccessful.

Sgt. Michael Fenske, a Washington policeman, has worked on the Speer case for 13 months, the last 10 of them on his off-duty hours. He said Speer left Washington intending to go to work for a company that the policeman does not believe exists. Fenske said he thinks that the mining company and job Speer was to fill were created by an impostor.

When SPeer's father stopped hearing from his son he hired Cunningham, the Oklahoma City private investigator. Cunningham discovered that a Michael Carr Speer had taken cut an Oklahoma driver's license.

The social security number, name and date of birth were that of Farlan Speer's, according to Speer's father, Washington police and Cunningham. But the description was of a man who was 5 feet 9, 160 pounds, with black hair and brown eyes.

In the months between Farlan Speer's disappearance and the sudden departure of the couple calling themselves Mr. and Mrs. Speer following the investigator's interview, a man with James Sheker's characteristics approached many business people, using Speer's credentials, looking for investors in a "coal degasification plan" and for personal employment, according to Washington police and others.

Sheker landed a job with Drum Construction Co., a San Antonio, Tex., firm, which put Sheker in charge of its Oklahoma operation for four months of 1976, according to police. As vice-president of the company, his name appeared on the company's letterhead as Michael Carr Speer, and he represented the company on business transactions across the country.

Sheker left the construction firm in the spring last year. The last message he is known to have sent was to a man who operates a job placement service for professionals in high-level executive positions, according to investigators. Sheker said he had found a job and thus no longer needed the man's services. The letter was postmarked in California.

Meanwhile 15 to 25 FBI agents nationwide, are looking for James Sheker in connection with the Prince William County fraud charge, in which Sheker allegedly obtained money for services as a civil engineer. The civil engineering certification number he used belonged to that of a retired engineer, police said.

There is no indication that Sheker was ever certified as a civil engineer, although he supervised construction of roads and water lines in the Dunfries area as a civil engineer while employed by the Montclair Development Co., according to Washington police.

Dorothy Sheker is living in Palm Beach Gardens, Fla., according to her stepfather, Ernest, L. Hogan, chairman of the board of People's Life Insurance Co. in Washington. He refused to disclose his stepdaughter's address or phone number, which is unlisted. Numerous other efforts to talk to her were unsuccessful.

Washington police have stopped looking for Farlan Speer. He is an adult, free to leave the city as he chooses, they said.

Oklahoma City police said they have no interest in the case, having no evidence that Farlan Speer was ever in their city.

"There has been no crime committed that we can prove at this time," Sgt. Fenske said, admitting it irks him not to be able to pursue the case.