The Christmas season has come early to Northern Virginia post offices, where federal elves are working long hours shuffling and delivering about 1 million more letters a day than they did this time last year, an increase of 25 percent.

Postal officials said yesterday that letter carriers and sorters have been asked to work six days a week, and 10 to 12 hours a day, to keep the mail moving swiftly on its appointed rounds.

In the Herndon and Sterling areas, where the increase has been the largest, carriers delivered mail on Veterans Day and two Sundays this month, officials said. In some neighborhoods, mail has been delivered three times a day to make more room at post offices.

Postal workers and officials said yesterday that the increase in letter volume is due to the area's increasing population and to earlier-than-usual bulk-mail holiday advertisements.

Eugene F. Smith, vice president of the Northern Virginia local of the American Postal Workers Union, said the U.S. Postal Service had aggravated the situation by waiting until now to hire temporary help.

Postal workers are "very dissatisfied," Smith said. "I get complaints every day . . . . People are just tired."

Concern about the mail volume, and complaints of delays in delivery, prompted Rep. Frank R. Wolf (R-Va.) to ask the postmaster general's Philadelphia regional office to review the situation.

In a press release this week, Wolf's office said he had received "a large number of complaints from Northern Virginia constituents about delays in delivery of both residential and business mail. In some cases, he has been told of mail that has never been delivered."

However, Smith and other postal workers and officials said yesterday that they did not believe there had been many delays in processing and delivering mail. They said they knew of no mail that had not been delivered.

This time last year, about 4 million pieces of mail were processed and delivered each day in Northern Virginia, compared with 5 million this year, according to Fran Ford, public affairs officer for the regional processing center in Merrifield.

She said that the 85 post offices and 55 post stations in Northern Virginia had 15,000 residences added to their routes this year.

Ford said officials are in the process of hiring about 200 carriers and at least 50 additional clerks for Northern Virginia postal facilities. Because of an unusually low local unemployment rate, however, attracting applicants has been difficult, she said.

At the post office in Herndon, clerk Shirley McClanahan said, "I've worked here for 18 years and I've never seen it quite so heavy." She said two groups of regional postmasters had been sent in recently to evaluate the office and to add postal routes.

"We just take it one day at a time," she said.