A gold pair of cuff links from President Lyndon B. Johnson and a tie clasp and other mementos from Soviet cosmonauts were among an estimated $30,000 worth of silverware, jewelry, and medallions stolen Saturday from the Potomac home of Sen. John Glenn (D-Ohio), Montgomery County police said yesterday.

Glenn, the former astronaut who became the first American to orbit the earth in 1962, yesterday said the thieves' haul included at least 40 of his most cherished family heirlooms and medals from his career as an astronaut and Marine Corps flyer, many of which he had planned on giving to a museum.

Police said they believe the theft, which occurred just five days after the 15th anniversary of Glenn's pioneering space flight, may have been the work of a gang that stole over $1 million in valuables from wealthy Washington area residents last year.

Montgomery and Fairfax County police believe the same thieves also are responsible for the burglaries last weekend of four other homes in affluent sections of the two counties. The thieves, known as the "silver gang" because of their penchant for silver and other valuable metals, are believed responsible for a number of burglaries up and down the East Coast from New York to Florida, police said.

"They didn't break up the house," Glenn said yesterday, "but they took many things of great sentimental value to me and my family. These things are really irreplaceable."

The similarity between how the silver gang ransacked homes in the area last year and how the Glenn home and the other homes in Silver Spring, Bethesda, and McLean were burglarized had been noted almost immediately by police.

"We can't say for sure, but it looks like them," said Montgomery County Police Sgt. Craighton Brantholder yesterday. "It really does."

The burglary occurred sometime Saturday afternoon or evening, police said, while Glenn was working at his Senate office and his wife was visiting the couple's daughter Lyn at George Washington University Hospital, where she was recovering from a minor operation. The thieves broke a windowpane of the master bedroom at the rear of the ranch-style brick house and then unlatched the window to gain entrance, police said.

The Glenns live on Belmart Road in the Potomac Falls subdivision of Potomac. The area is one of imposing, expensive homes set on two-acre lots. Glenn paid about $150,000 for his home, an aide said.

Brantholder said police had talked to a neighbor of Glenn's who had seen a strange man in the neighborhood Saturday afternoon, but would not further discuss the investigation.

Police said the thieves methodically searched first the master bedroom, then the home's other three bedrooms, family room, dining room, and living room. They took no appliances, clothing, or any of Glenn's bronze medals. Only those valuables of gold and silver were taken, police said.

Glenn said he and his wife, who returned home about 8:30 Saturday night, may have caused the thieves to flee prematurely.

Glenn who walked to the front door while his wife was still parking her car in the garage, said he found the front door unlocked and several gold medallions and cufflinks neatly laid out on the living room floor.

"They had been taken out of their cases," Glenn said. "It looked as if they were being inspected to determine their value."

Glenn said he is considering offering a $1,000 reward for information about the burglary. "There's no complete listing (of the stolen awards and medals)," he said. "I never made an inventory. Of course, now I wish I had."

Details of the other burglaries were not available yesterday afternoon, but there seemed little doubt among police and FBI officials contacted yesterday that the silver gang was responsible.

In the first five months of 1976 the discriminating burglars broke into 110 affluent homes in the city of Alexandria, and Arlington, Fairfax, and Montgomery counties. In all burglaries they demonstrated an ability to distinguish between sterling silver and silverplate, between real gold and costume jewelry, between real gems and imitation stones.

Other items stolen from the Glenn home included his first pair of gold Navy flight wings, a pair of Chinese ivory carvings of pastoral scenes, and all his wife's jewelry, police said.