Girl Scout cookies are sweet, but for Elizabeth Brinton the taste of success, with maybe just a touch of unspoken revenge, is sweetest of all.

Finally, after selling 11,200 boxes of Girl Scout cookies, the 13-year-old Falls Church girl got her just reward yesterday: recognition as the best cookie seller around, not to mention a new personal computer.

For the past several years, Elizabeth could do nothing but a slow burn as another girl scout, Markita Andrews of New York, grabbed the spotlight for her cookie-selling prowess. There were appearances on Good Morning America and Silver Spoons, the television series starring teen heartthrob Ricky Schroeder. The New York Times even dubbed Markita the greatest cookie seller of all time.

All this time, Elizabeth said she was selling even greater numbers of cookies. The problem was that her local Girl Scout council didn't keep official figures on individual sales, the idea being to emphasize the group benefits of selling, said Sonia Snyder of the Girl Scout Council of the Nation's Capital.

The council changed that policy this year, and even offered an inducement to encourage sales: a personal computer donated by the Tandy Corp. to the girl who sold the most.

Brinton's victory, proclaimed at an award ceremony yesterday, was no surprise. After all, her career total, after eight seasons of cookie selling, is now over 36,000 boxes.

But Elizabeth was also able to put to rest any doubts over who is the best cookie seller. Arch-rival Markita sold only 4,044 boxes of cookies this year, according to the Girl Scout Council of Greater New York.

Elizabeth said she routinely worked 40-hour weeks selling cookies this spring, most of those hours camped out near either the Ballston or Crystal City Metro stations.

People who were not in the mood to buy cookies traveled through those stations at their own risk. Elizabeth is an unabashed advocate of the hard sell.

"I push a lot. I'm not quiet," she said. "Sometimes they would try to sneak past you, and you look them in the eye and make them feel guilty. After all, the cookies taste good, and it's for a good cause."

A group of local insurance salesmen was impressed enough, Elizabeth said, to invite her to give a speech at their annual convention earlier this year.

But Girl Scout officials say they like Elizabeth because she's interested in more than just the competition. On Saturdays this spring, Elizabeth volunteered her time at the Girl Scout cookie store at 18th and M streets NW, even though this didn't contribute to her contest totals.

"She's really the model scout. We're all very proud of her," said Girl Scout spokewoman Jacqueline Browne.

As talented as Elizabeth is, she has yet to achieve her highest goal: Even with the help of a letter on her behalf from her congressman, Frank R. Wolf (R-Va.), President Reagan did not buy any cookies from Elizabeth this year.