NEW YORK (AP) _ Markita Andrews is more than 100 times better than the average Girl Scout - when it comes to selling cookies.

Just how good is Markita?

Well, in six years, she's sold 15,500 boxes of cookies during annual drives - 8,000 boxes alone in 1984. And in this year's three-week-long sales drive that ended Monday, Marita sold 2,196 boxes of cookies.

In addition, the 13-year-old has sold nearly 10,000 more boxes when she delivers her orders and collects from her customers.

In 1984, each of America's 2.3 million Girl Scouts sold an average of about 60 boxes, according to the Girl Scouts of the United States of America. For $2 a box, the Girl Scouts sell the top-selling Thin Mints or six other varieties of cookies.

Markita sells most of her cookies to neighbors among the 10,000 residents of an eight-building apartment complex on Manhattan's Upper West Side, where she's something of a celebrity.

Her selling style is persistent but polite. ''You just can't chat. You have to ask for an order,'' is the way she once summed it up.

During the cookie drive, Markita takes up her post, in the lobbies and at the mail boxes of the Lincoln Towers buildings, for up to 2 hours nightly and each weekend.

''It's best to go where the people are,'' she explained.

Markita has been immortalized in ''The Cookie Kid,'' an 11-minute sales- training film produced by Walt Disney. The film has been shown to more than 100 corporations worldwide, including IBM, AT&T, Exxon and West German automaker BMW.

The 98-pound girl has a trust fund for her college education based on ''honorariums'' she often gets to appear before corporate groups to tell them how she became the nation's most famous Girl Scout. Her travels to speak to those groups have taken her to Bermuda, Canada, California, Hawaii and Florida.

But some Girl Scout officials are critical of Markita's zealous approach to selling cookies.

''With the competitive approach (used by Markita), we believe some kids will lose sight of Girl Scout goals,'' said spokeswoman Gloria Rella of the Girl Scouts of the United States of America.

''Selling cookies is really fun 'girl' activities and we're working hard to keep it a Girl Scout fund-raiser that isn't competitive,'' said Bonnie McKuen, media services director for the national council.

However, Markita said, she really likes selling.

''I meet lots of people and learn a lot about business. And I want to sell something when I get older.''

''I probably could sell anything if I really wanted to,'' the 5-foot girl said. About the only thing she has ruled out is guns. ''I'd want to do something more to help people.''

But she admits she is hurt by the criticism.

''I wish they'd see that I'm just trying to help the Girl Scouts. I'm enjoying myself. It's not like I'm being forced,'' she said.

But some say she works so hard because of the influence of her aunt, Meredith McSherry.

Mrs. McSherry accompanies Markita on every trip, formulates a selling strategy and collects money for the girl so that she can concentrate on sales.

''I may be a little bit pushy sometimes,'' Mrs. McSherry admitted, ''but I really think I've disciplined her in the right way.''

Mrs. McSherry has been close to Markita since the girl moved to New York with her mother eight years ago after her parents separated in Anaheim, Calif.

Mrs. McSherry, who has no children of her own, keeps a scrapbook on Markita, replete with a 4-page tally of Markita's success since she entered the Brownies at age 6.

The scrapbook shows pictures of Markita selling Girl Scout cookies in Newsweek and People magazines, articles from The New York Times and business publications' analysis of her sales techniques.

Markita's success creates a logistics problem each April for tenants in Lincoln Towers: a Mack truck filled with boxes of cookies ordered by her customers clogs delivery lanes for hours until the cookies are unloaded and carted into her apartment, Mrs. McSherry said.

And for the three weeks or so while Markita delivers the cookies to her customers, Mrs. McSherry said her apartment ''is wall-to-wall cookies.''

But it's all worth it, Markita insists.

''Listen,'' she said in the soft voice that has sold tons of cookies. ''This really is fun. So won't you buy a box or two for your friends or family or for the office?''