Using a device that looks like the combination of a camera and a pair of binoculars, two law enforcement officers combed the woods of western Alexandria yesterday in search of the body of an Alexandria woman missing for a month. They did not find her.

The device, called an infra-red sensor or a hand-held thermal viewer, defects body heat and had most often been used in the jungles of Vietnam to detect hidden persons, according to Alexandria Police Capt. Clyde Scott.

Alexandria police borrowed the sensor through the U.S. Customs Service to help them in their investigation of the deaths of three young Alexandria women and the disappearance of another. The four women all lived within a mile of one another in the Landmark area of the city along In-TERSTATE Rte. 95.

The sensor which costs about $18,000, is intended to help police detect a decomposing body that may be covered or buried in a shallow grave.

The sensor gives the person using the device an instant image, like a pitcure negative, of the object giving off the heat, according to Lt. Otis Pettit. He searched for the missing person, Aletha Byrd, who police eblitve is dead, along Holmes Run Creek behind the Hamlet apartments.

Alexandria police have resorted to the sensor because "our regular starches have turned up nothing," Scott said.

Meanwhile, in Arlington County, police are searching for the slayer of an Arlington real estate agent and his fiancee, who were found dead Sunday in the garage of the man's home at 1201 N. George Mason Dr., Arlington police said yesterday they have no suspects in the killings of Alan W. Foreman, 26, and his fiancee, Donna Shoemaker, 21, of 4921 Manitoba Dr., west of Alexandria in Fairfax County.

Seven homicide-robbery detectives and uniformed officers spent most of the day in Arlington searching for fingerprints in the two-storey black-trimmed brick colonial home. Police said they will not know what caliber gun was used to shoot Foreman and Shoemaker in the face and chest until an autopsy report is completed today.

"We're going on all the theories," police spokesman said. "There's nothing of substance to say there was a burglary and that they (Shoemaker and Foreman) surprised (burglars)." Nothing seemed to have been taken from the house, the spokesman said.

"The only thing we've ruled out is there was a maniac running down the street shooting people," the spokesman said. Neighbors said Miss Shoemaker sometimes lived in the house with Foreman, the police spokesman said.

Alexandria police have said Aletha Byrd, 34, who lived at 5445 N. Morgan Street in the Holmes Run Park apartment complex, was reported missing on April 10. Her car was found last week in a nearby parking lot.

Two other Alexandria women who lived in the Holmes Run Park complex was found dead last week by police. Gladys R. Bradley, 27, was found April 30 in Holmes Run Creek. Jeanette M. McClelland, 24, was found last Thursday afternoon in a culvert, less than a mile from where Bradley's body had been discovered.

Last August, Aura Marina Gabor, 24, was found strangled to death in the same section of Alexandria. That case has never been solved and Alexandria police have reopened their investigation in light of the Bradley and McClelland deaths.

McClelland apparently was stabbed to death, while police tentatively have ruled Bradley's death as a drowning. They are awaiting an extensive toxicology report on Bradley's death.

Alexandria police said they still have no direct link connecting the three deaths and the disappearance of Byrd, other than the proximity of where the bodies were found and where the women lived.

Police are canvassing western Alexandria, interviewing everyone in the apartment buildings for information about the deaths and disappearance. They said they want information about any suspicious person seen in parking lots late at night, suspicious cars, or anything else that may be useful, and have asked all apartment occupants not personally interviewed by police - or anyone with information - to call police at 750-6542.

In the Arlington case, the bodies of Foreman and Shoemaker were found at 9:33 a.m. Sunday by police, who were called by a neighbor who had looked in the window and saw Foreman's body, county police said.

FOREMAN WORKED AT TOWN and County Properties. Ray Oliva, the firm's Arlington sales manager, said that Foreman "had a promising career. He found his niche." Foreman had worked there for two years and had make $500,000 worth of sales last year, Oliva said.

"It's quite an achievement," Oliva said of Foreman's sales record. He knew his business. I know he planned to stay in the real estate business."

Residents of Miss Shoemaker's Alexandria apartment building said yesterday they did not know her. She had worked as a secretary in the District of Columbia, the police spokesman said. Oliva said Miss Shoemaker had quit her job with an oral surgeon and was looking for employment.