For radio stations, the fight for listeners has moved from the morning commute to the workplace.

With a dwindling number of people at home during the day and more behind a desk, stations around Washington have launched a variety of promotions designed to attract listeners who are working.

Some encourage office employees to use their facsimile machines to play contests featuring such grown-up prizes as free day care or a month's rent. Some are shifting formats to make them more welcome in the office. Others are delivering lunch to companies that don't consider the radio an intrusion.

"The new marketing battlefield for smart radio stations is a person's desk," said Walter Sabo Jr., who advises radio and television stations on promotional strategies. "If you want to reach people during the day, you have to go to the office."

Given recent demographic shifts and the huge number of clerical and white-collar workers in the Washington area, that's pure common sense.

Midday used to be a vast wasteland when a large chunk of listeners were stay-at-home wives who were more likely to watch a TV soap opera or tune out completely.

But with two of every three adult women in the region now holding a job, they've become a marketing opportunity. Moreover, most office workers are between the ages of 25 and 54, the category most coveted by advertisers.

Although morning drive-time still attracts the largest radio audience, listeners are increasingly tuning in from 10 a.m. to 3 p.m.

Nationally, people age 25 to 44 listened to the radio an average of eight hours, 49 minutes a week at midday, an increase of 43 minutes since 1986, according to a study by the Katz Radio Group.

Locally, such FM stations as WMZQ, WPGC, WASH, WGMS and WLTT had better ratings during the midday hours than in the commuter period of 3 to 7 p.m., according to Arbitron Ratings Co.

Efforts to pump up their daytime audience ratings have compelled stations to finetune their formats. WPGC-FM usually plays upbeat dance and urban pop music in the morning and evening, but it programs older and softer tunes during office hours and instructs its midday deejays to tone down their chatter.

"The idea is to be more passive and familiar," said WPGC program director Dave Ferguson. "The person working at the hair salon or behind a typewriter can't be jolted by something that will take their mind away from work."

WPGC's strategy seems to be working: The station attracted the largest midday audience of any station during the past three months, according to Arbitron.

Arbitron itself may have encouraged such targeting by making a subtle but important change in the way it measures radio audiences. The company recently began asking its survey participants to indicate how much listening they were doing at work, something it had never asked before.

Some radio executives believe that this change drew advertiser attention to that segment of the day.

While dreamy "easy listening" music has traditionally been most welcome in businesses, even Top 40 stations have tried to wedge their way into offices.

But Bob McNeill, the acting general manager of country music station WMZQ-FM, argues that "beautiful music" and soft rock are merely background music that listeners aren't really paying attention to.

On the other hand, someone's listening: WGAY-FM, an easy-listening station, was the second-highest rated station at midday after WPGC.

Several employers said they didn't mind radios in the office -- provided the music didn't distract workers from doing their jobs.

The only place that TRW Systems Integration Group of Fairfax strictly bans radios, in fact, is in its high-security areas where an ordinary radio could be juryrigged to transmit classified materials.

A number of federal agencies permit civil-service workers to tune in. Indeed, one of the recent winners of WLTT-FM's catered lunch contest were workers at the top-secret Defense Mapping Agency.

Some of the unions that represent federal workers have won radio privileges for their members in bargaining with the government, said Barry Shapiro, the acting chief of the Office of Personnel Management's labor-relations division.

"It would be unlikely that someone sitting at a public service desk in the IRS would be authorized to have a radio," Shapiro said. "But in offices where there is little or no contact with the public, say, where people are examining Social Security claims or tax returns, it might be acceptable as background music."

Government tax examiners rocking out to Led Zeppelin? These days, that's sweet music to people in the radio business.