Thousands of Northern Virginians have taken advantage of an experimental program that enables them to electronically change their mailing addresses, buy personalized return-address labels and print messages on pre-stamped cards at special kiosks similar to automatic teller machines, according to results released this month.

During the first three months of operation in Northern Virginia, Postal Buddy machines have been used by 25,256 people and businesses. The Postal Service is considering continuing the experiment an additional six months, according to a spokeman for Postal Buddy. Between August and October, more than 13,000 people used the machines to change their addresses -- 158 percent over original projections.

Postal Buddy can electronically change a person's address with the Postal Service, selected magazines, catalogues and credit card companies.

When people change their addresses, they use a computer keyboard at the kiosk and enter the appropriate information. The information is relayed to the Postal Buddy company and is available to the company's subscribers, the company said.

The system is being test marketed only in Northern Virginia, Postal Buddy President Sidney Goodman said. That area was chosen because it is "a definable area close to postal headquarters {in Washington}, so it would be easy for everyone involved to keep tabs on it," Goodman said.

The transient nature of the Northern Virginia area also was useful to evaluate the program.

"We didn't want to test in an area where there was an extremely low turnover" of residents, Goodman said. "The average would have been more desirable, but the Postal Buddy system is supposed to save the Postal Service money."

Each year, more than 39 million change-of-address cards are processed by the Postal Service nationwide, and the cost of handling 2.25 billion pieces of mail that cannot be delivered because of incorrect addresses exceeds $1.3 billion, the company said.

Postal Buddy said it hopes eventually to handle about half the change-of-address transactions.

Goodman invented Postal Buddy. The business started when he created a return-address label manufactured using a high-speed laser process.

In 1986, Goodman started Welcome Labels Corp., which sold return-address labels to apartment owners to give to new residents.

The forerunner of Postal Buddy was a machine Goodman developed to sell return labels, and in December 1988 he approached the Postal Service about using his machines.

How popular Postal Buddy would be was hard to assess, Goodman said.

He said the machines at first seemed to be complicated for use by the public.

"We didn't know when we put them out there exactly what would happen," Goodman said. But he added that "people were attracted to it."

As for the service being used much more than originally projected, Goodman said, "It's hard to project something that's never been done before."