Now that NBC has extended the political drama ''The West Wing'' for an entire season, Allison Janney -- who plays the White House press secretary -- can finally relax. Earlier this fall, she'd been studying the Nielsens the way James Carville does the results of the New Hampshire primary. ''I never thought I'd be obsessed with ratings,'' says Janney, 39, a veteran of stage and such films as ''Primary Colors'' and ''The Object of My Affection.'' ''But the first night before our numbers came out I was so nervous I didn't sleep at all. You put so much work into the show, it feels worse than it does opening night on Broadway when you're waiting for the reviews. In TV, you feel that every week.''
''West Wing'' has managed to be one of this season's few new shows to hit the top 20. Of course, if Nielsen counted repeat viewings, it could have double the ratings: With ''Sports Night'''s dialogue-happy Aaron Sorkin at the creative controls, viewers need to tape and rewind to catch up with the rapid-fire banter, and Janney thinks that challenge has helped keep the show going. ''The audience is always a little behind, and that's what gets people hooked,'' she says. ''They want to keep following because they say, 'Wait a minute, I'm not stupid. I can get this.'''
Janney promises that as the season progresses, ''Wing'' will start delving more into the characters' extracurricular lives, giving viewers a break from the initial crash course on Oval Office politics. Of course, because Sorkin likes to keep everything in the workplace (witness the two relationships currently flowering on ''Sports Night''), any love affair will have to come back to 1600 Pennsylvania Avenue. Janney's character, for example, will begin a fling with a White House pool reporter (played by ''thirtysomething'''s Timothy Busfield), which can only compromise her allegiances. ''The more Aaron gets into the personal lives, the more interesting it will be,'' she promises. ''People don't watch 'ER' to see the operations.''