A cache of jewlry, silver, antiques, furs and weapons filling 51 cardboard boxes has been seized by police from the plush Great Falls, Va., home of Bernard Charles Welch Jr. -- an escaped convict, alleged master thief and accused killer of Dr. Michael Halberstam.

Police reported yesterday that the allegedly stolen property, valued by one law enforcement source at $2 million, was found Saturday night in the boxes in two basement rooms of Welch's secluded home. The tan brick ranch house was purchased last year for $235,000 in cash.

At the same time, Montgomery County police said Welch is the "prime and outstanding suspect" as the "Standard Time Rapist" who allegedly burglarized more than 100 fashionable homes in recent years throughout the Washington area and raped three women at gunpoint, one of them a 74-year-old homeowner. The Standard Time Rapist was so dubbed by police because he struck only between 6 and 10 p.m. during the winter.

Welch's suspected criminal involvement was so far-reaching, law enforcement sources said, that the investigation into what one officer termed a "one-man crime wave" will be handled jointly by all local suburban police authorities, the Federal Bureau of Investigation, The Prince William and Frederick county police and police from Duluth, Minn., where Welch lived part of the year.

Described by the Police and his Great Falls neighbors as a sophisticated and seemingly well-educated man, the 40-year-old former plumber and antique dealer was arrested Friday night after he allegedly shot nationally known cardiologist and author Dr. Michael Halberstam. Welch is being held in D.C. Jail, pending arraignment in D.C. Superior Court this morning.

Police searched Welch's home Saturday night at 7:30 after discovering allegedly stolen property in his $39,000 gray 1980 Mercedes, which was towed from Halberstram's Northwest Washington neighborhood. Six officers from the Fairfax County, Montgomery County and District of Columbia police departments seized the 51 boxes.

They were stuffed with complete sterling silver settings, silver cadleabras, urns, trays gold jewlry and ornaments, mink, sable and other fur coats, antique clocks, carved ivory and blown-glass perfume bottles, collectors' dolls, porcelain Hummel figurines, handguns, rifles and muskets, according to Faifax County police spokesman Warren Carmichael.

As the officers laded the items onto and 18-foot panel truck, Linda Susan Hamilton, a woman neighbors knew as Welch's wife, and her three children looked on silently. Hamilton, who told police she could not account for the origin of the goods, offered no resistance, police said.

Police sources said that she apparently never knew that "Norm Hamilton," the most recent of numerous aliases police allege that Welch has used over the years, was not the man he pretended to be.

"She was a victim as much as anyone else," one law enforcement source said. "She was not involved. She thought Welch was a wealthy stock and real estate man, just like everyone else did."

After working all day yesterday, Fairfax police had catalogued items from five of the boxes. Carmichael said it will take a team of Fairfax officers at least three days to catalogue the remaining items. Police from other area jurisdictions then will be asked to try to match the property with items taken in burglaries in recent years.

"It s absolutely impossible to evaluate home many victims are involved here" he said.

During the last four years, a man who Montgomery police say matches Welch's description was sought in the Washington area as the suspect who came to be known as the Standard Time Rapist.

Described by police at a February 1980 press conference as "articulate and seemingly well-educated" the assailant was known to wear casual clothes, a mustache and neatly trimmed hair. He carried a revolver and chose only the most fashionable single-family homes throughout the area to break into, usually from a rear entrance.

A Montgomery County police spokeswoman said yesterday that Welch "was identified as the suspect in the Standard Time Rapist cases four years ago; we just didn't know where he was," Police refrained from identifying Welch at the February press conference, the spokeswomen said, to avoid alerting him.

In four of the estimated 100 burlglaries, the man was surprised by returning homeowners. He raped three women and attmepted to rape a fourth, police said. In four other cases, victims were bound while their assailant bragged, "I've killed people," investigators said.

Snipping the telephone lines of his target homes before entering, the burglar would strike in Montgomery County one night and Fairfax the next, police said.

"The man is notorious," Montgomery County police detective Jack Toomey said at the February press conference. "Most burglars do not want their victims to see them.This guy doesn't care. He probably considers himself a master criminal. He'll stop at nothing."

Welch and Linda Susan Hamilton had met each other several years ago in Washington, acquantances said yesterday.

The couple rented a large house on a five-acre estate in the prestigious South Down Farm development in Great Falls before buying the tan brick rambler at 411 Chesapeake Dr. in June 1979.

The former owner of the Chesapeake Drive home, Louis Sorrentino, said in a telephone interview from Denver yesterday that the couple contacted the Long & Foster real estate company in McLean 24 hours after the house was listed for sale.

"He said he didn't want to haggle over the price, that he wanted to move in right away," Sorrentino recalled. "They said they had driven by the house once or twice before and had admired it. I got the impression they were quite wealthy. He said he owned real estate in Washington, homes and apartment buildings, I think he said."

According to Sorrentino, it was Linda Susan Hamilton -- pregnant with her second child -- who acutally purchased the house with a $235,000 check.

"Criminal or not," said one Long & Foster spokesman yesterday, "the color of his money was green."

Sorrentino said that his impression of the couple was "that he was older than she, but that she was the one who did all the business. He didn't have much to say, although he was extremely friendly."

Another acquantance who knew the Hamiltons at the time said, "They seemed like an unusual couple. He told me he had been a plumber at one time."

"Norm Hamilton," one former acquaintance recalled, always wore dungarees and work shirts, or leisure-type suits.

The couple spent last summer in Duluth, Minn., neighbors said, where their summer house was located. According to one real estate agent, Linda Susan Hamilton said her father lived in Duluth and was a wealthy businessman.

One law enforcement source said yesterday that the couple owned a business there and kept more than $700,000 in a Duluth bank.

"I remember being called by an interior decorator from Duluth," said Sorrentino, "who wanted to know more details about the house. I suppose they were bringing furnishings and things from there."

Sorrentino also said his former neighbors had told him "Norman Hamilton" had already spent nearly $500,000 on an addition that nearly doubled the size of the country rambler by adding an enclosed swimming pool and extra bedrooms.

Last October, Welch called a Nationwide Insurance office in Northern Virginia, inquiring about a homeowner's policy that included insurance against theft and burglary. "He told me he was a coin dealer, had paid for his house in cash and wanted $175,000 worth of insurance in his wife's name," the agent said yesterday. "Actually, I don't think he said it was his wife, he just said her name: Linda Susan Hamilton."

But the insurance policy was never written, the agent said. "He wouldn't give me any more information about himself. It was strange. I said I couldn't write the policy."

Welch also installed an elaborate security system at the Chesapeake Drive home, complete with closed-circuit television cameras at three separate entrances.

Police say that Halberstam surprised Welch Friday night during an attempted burglary. Halberstam was shot twice in the chest, but managed to run down his assailant with his car while attempting to drive himself to the hospital.