Elizabeth Brinton, the Falls Church ninth grader who combined girl-next-door cuteness with brass-tacks business acumen last year to set the unofficial record for the most Girl Scout cookies ever sold, was accused yesterday of going one step too far to sell her cookies.

By selling President Reagan seven boxes of cookies at a White House ceremony Thursday, Elizabeth ignored a nationwide embargo on selling cookies before the opening of selling season yesterday, her critics -- mothers of other girl scouts -- charged.

"This is someone who is supposed to be such a terrific girl scout . . . . Girl scouts are supposed to live by the rules, and the rule is that you were not supposed to take orders until today," said Brenda Albert, a Reston mother who is the cookie manager for her daughter's Brownie troop 2164.

A spokeswoman for the Girl Scout Council of the Nation's Capitol said yesterday that the organization received calls from girl scouts and parent leaders complaining that Elizabeth, 14, had unfairly jumped the gun.

The Brintons and Girl Scout officials brushed aside the charges yesterday, saying that they were stuck with the date the president gave them. "You don't ask the White House to change a date," Noel Brinton, Elizabeth's mother, said.

Said Elizabeth: "I feel this is perfectly all right if he's the president. I mean, goodness, I've been wanting to do this for a long time."

In any case, she isn't prone to letting her critics distract her for long. Elizabeth, who sold 11,200 boxes last year, said she intends to break her own record and has an assortment of tricks to help her do it. Among them: speaking to sales conventions and accepting cookie order forms in lieu of cash.

Both of which probably will be all right -- as long as she doesn't break any more cookie embargoes.