At 5 feet tall and 100 pounds, with a layered hairdo and a sparkling smile, Sarah Wright has looks that have gotten a lot of people into trouble.

The 20-year-old Fairfax County police cadet and another youthful-looking cadet walked into 200 stores countywide for three weeks in May, poised to buy wine and liquor. Sales clerks in almost half the stores sold them the beverages without checking their ages, resulting in the arrests of 90 persons for illegal sales of alcoholic beverages to minors.

"I'm appalled," Capt. Richard J. Rappoport, commander of the Reston District Station, said yesterday in announcing the results of the undercover investigation. Rappoport said the police department, which began the operation because of citizen complaints, said it had expected that about 10 percent -- not a whopping 45 percent -- of the stores would violate the state wine and liquor sale laws.

"Frankly, we are very concerned that minors were able to purchase alcoholic beverages unchallenged at nearly half the establishments checked," said Maj. E.A. Stevens, commander of the police department's patrol bureau. "Obviously, we will have to continue our enforcement efforts."

The businesses with the highest percentage of violations included Peoples Drug Stores, where arrests were made at 12 of 21 stores; Drug Fair, with eight arrests at 15 stores visited, and Dart Drug, with eight arrests at 16 stores visited. Violations were found at six of 18 Giant Food stores. Police arrested sales persons at six of the eight Virginia Alcoholic Beverage Commission outlets visited.

Sue Challis, a spokeswoman for Giant Food, said, "We were one of the first to come up with a formal program to train employes in how to be in compliance with the law." She said a reminder for employes to check identifications is built into the stores' checkout scanner system, and added, "Our record up until now has really been exemplary."

Virginia law requires persons to be at least 21 years old to purchase wine and liquor legally. The law was changed two years ago, setting the age limit for beer purchasers at 21, but a grandfather clause in the law allows persons born on or before July 2, 1966, to purchase beer.

The police department directed its cadets to purchase wine at retail establishments and rum at the state-owned Alcoholic Beverage Control stores. The operation was timed to coincide with high school proms and graduations.

Wright, a student at Northern Virginia Community College who plans to attend the police academy next year, was selected for the undercover operation because of her youthful looks, according to law enforcement officials.

Surrounded by bottles of Riunite, Bacardi rum and California Cooler that she had purchased, Wright told reporters yesterday that she was surprised at how easy it was to purchase the liquor and wine. Once the bottles had been bagged, a plainclothes police officer in the store would arrest the sales clerk on the misdemeanor charge.

It was then that the youthful looking cadet was accused of looking old.

"One lady said I had wrinkles," said Wright, who visited as many as 38 stores in one day. "They said, 'She looks so old to me.' One thought I was about 28 to 30. It's been an experience."

As the operation progressed, stores began circulating her description, Wright said. Police then added a second cadet, David A. Mulvey, 19, a gangly part-time student.

"I was dressed like this and the guy didn't even ask me for identification ," said Mulvey, modeling his undercover uniform: Nike shoes, corduroy pants and a polo shirt. "I was kind of nervous at first, until I got the hang of it."