After 13 months of coming and going from the same tan brick condominium building at 15111 Glade Dr. in Silver Spring. Len Fussilo arrived home yesterday to discover that the street number on his building had been assigned to the red brick unit next door.

Not only that, but Fusillo noticed that street numbers on all four condominium buildings on his block in the Rossmoor Leisure World community had been switched. 15100 is now l5lll, 15101 is 15121, 15111 is 15101 and 15121 is 15100.

"It's like moving without moving," he said.

"How would you like to come home and find out that someone else had your address?" he said.

The unannounced change of street numbers on four Glade Drive buildings occurred yesterday.

The numbers have been wrong for five years. When the block was built workers used the wrong plan for street number assignments, according to the current president of Rossmoor Construction Corp., which is developing the community for people over 50.

The numbers were posted incorrectly, but no one discovered it until last year, when fire and rescue workers complained to the Montgomery County Planning Board that they were delayed on two occasions in responding to calls on Glade Drive because of the out-of-sequence street numbers.

David R. Hudgel Jr., who assigns house numbers and street names for the planning board, said that despite pleas from Rossmoor residents for an exception to the rules, "we had to insist on uniformity."

"I'm willing to go more than halfway, if I can," said Hudgel, "but because of these delayed emergency responses we just couldn't have this. Odd numbers were across the street from odd numbers."

Lewis Letson, current president of Rossmoor Construction Corp., said he had no choice" but to acquiesce to the planners' directive.

Although some residents had heard that a change was possible, they were not notified if or when it would happen. Then suddenly, the new numbers appeared yesterday.

"The people are going crazy. They're old and they're excited," said Fusillo. "Their addresses and the addresses on their deeds, wills, social security cards, business stationery, all their legal papers, phone numbers, magazine subscriptions and so on don't match. I was 15111. Now I'm 15101. . . "