Before he was sentenced yesterday to 25 years in prison, Michael Montrose, the real estate agent turned burglar who stole an estimated $300,000 from nearly 100 Northern Virginia homes, said he was sorry.

"I'd like to apologise to all the people of Fairfax County for what I've done," said Montrose, a thin, bearded California native described in court yesterday by his attorney as a "terribly, terribly lonely young man."

"I have no excuses," said the 37-year-old college graduate and former computer programmer who became known as the "lock box" burglar. He said no amount of restitution or any length of imprisonment "can make up for what I've done."

What Montrose did, according to police, was use his real estate saleman's key to open the small metal lock boxes that are placed on thousands for sale homes and gain entrance to the homes with the keys kept inside the boxes.

Once in the homes, police said, Montrose stole furs, jewelry, silverware and other items of value that could not easily be traced. The burglaries occured from January unitl May, when Montrose was spotted inside a Springfield house by a 15-year-old youth who called police and let air out of the tires on Montrose's car.

Fairfax Country Circuit Court Judge Lewis D.Morris, imposing what he called "substanial punishment," sentenced Montrose to serve consective five-year prison termsfor each of the five counts of burglary to which Montrose pleaded guity on Sept. 11. Montrose, who ha no criminal record before his arrest in May, could be eligible for parole in six years.

Before yesterday's sentencing, Montrose's attorney, John H. Treanor, turned over to the court $17,700 the selling price for a shipment of stolen silver settings that Montrose had sent to New York City and had melted down.

The money, part of about $200,000 in stolen goods that Montrose turned over to police, will be held by the couutry and burglary victims can file suit against Fairfax Country to recover their losses.

Judge Morris said the money will be awarded on a "first-come, first served basis." Deputy Commonwealth's Attorney Steven A. Merril said there is also a "considerable amount" of stolen property in the police property room that is still unclaimed.

"But claiming it is not easy," Merril said. "It's hard to find with a spoon here and a fork there."

In pleading yesterday for mercy for Montrose, Treanor pictured his client as a lonely and enigmatic man.

Treanor said Montrose, who was dressed in a faded blue short- short sleeve shirt and faded blue slacks without a belt, came a "safe harbor" with his family in California, passed through several frustating computer jobs in his home state and arrived in Northern Virginia as a man with "no convictions."

Montrose lived in an apartment that was "sparsely and coldly furnished,"Treanor said. The attorney called Montrose "the loneliest human being I've ever met" and added that his client's crimes were "stupid.

"Perhaps in a very perverse way Minchael Montrose wanted to be caught," he said.

Prosecutor Merril said Montrose's crimes were far from stupid.

Police have said that Montrose drove around in quest for homes to burglarize with two map books and a computer listing of homes for sale in the Virginia suburbs. The maps showed homes selling for $90,000 or more, Merril said.

"He knew what homes he wanted to hit. He took only items that were not traceable," Merril said.

The prosecutor said Montrose coperated with ploice after he was caught.

Montrose had tried to flee from th scene of the Springfield burglary in his car with the flat tires, but was apprehended after his car turned over, spilling jewelry and over, spilling jewelry and other stolen items on the ground.