Michael Montrose, a tall, slim Californian, got his start in the Washington subsurbs' booming real estate business on Jan. 23.

On that day he received both his Virginia real estate license and a key to lock boxes which the region's real estate salesmen place on hundreds of homes that are for sale. Inside the boxes are individual keys that will unlock the homes.

Armed with two map books and a computer listing of homes for sale in the Virginia suburbs. Montrose, 37, would go about his work, noting all the homes costing more than $90,000 each and then checking those he had visited.

But Montrose's interest's were not in selling the houses, a police investigator told a Fairfax County judge yesterday. During a five-month period after he was licensed Montrose entered more than 100 homes and stole between $200,000 and $300,000 worth of furs, jewelry, silverware and other items, said detective Thomas Lyons Jr.

Montrose, a college graduate who moved to the Washington area from Los Angeles in September, pleaded guilty yesterday to five burglaries in Fairfax County. He could received up to 20 years in prison for each of the five burglaries.

Fairfax Circuit Court Judge Lewis D. Morris set sentencing for Nov. 9, after he reviews a presentence report on Montrose.

Because Montrose could receive up to 100 years for the five burglaries, Fairfax Deputy Commonwealth's Attorney Steven A. Merrill said he saw little need to charge Montrose with other burglaries.

The burglaries occurred in Alexandria, Falls Church, Fairfax City and Prince William, Arlington, and Fairfax counties between the end of January and May 26 at houses equipped with "lock boxes," Lyons said.

Police recovered much of the stolen property, which included typewriters, tape recorders, microscopes and suitcases, from Montrose's car, his home at 2758 Hyson La., and a rented storage area in Alexandria.

Police have said Montrose,who worked as a part-time agent for Century 21 Rowan and Estes Inc. of Falls Church, intended to sell the merchandise and had sold some before his arrest.

At yesterday's hearing, Lyons testified that Montrose's arrest on May 26 and after 15-year-old Kenneth Arthur warned police that he had discovered a man in his home at 6419 Brentford Dr., Springfield.

Lyons said Arthur discovered the man in his parents' bedroom "going through their belongings." The youth ran to a neighbor's home, called police, and then let the air out of one of the tires on Montrose's 1978 Datsun, the officer said.

As Montrose was leaving the house, he spotted a police officer responding to Arthur's call and was chased for a mile and a half before his car turned over, spilling jewelry and other items over the intersection of Keene Mill and Rolling roads.

Lyons said Montrose told police about the other burglaries he had committed and where they could recover some of the stolen items.

The detective said one woman, whose home had been burglarized on the same day Montrose was arrested, had also discovered Montrose in her home but "didn't think anything about it" since Montrose was a real estate agent. Only after police recovered items taken from her home did the woman realize it had been looted, Lyons said.

John Trainor, Montrose's attorney, told the judge that his client denies allegations that he burglarized more than 100 homes, although Montrose concedes that "there were many homes in excess of five." Trainor also said he believes that the police estimate of the value of the stolen property may be inflated because ofinsurance claims.