David B. Harrington, the former Silver Spring private school principal and a Montgomery County Big Brother of the Year, pleaded guilty in Montgomery County Circuit Court yesterday to six counts of child abuse and one count of felony theft.

In exchange for his pleas, the state's attorney's office agreed not to prosecute Harrington for several other alleged sex crimes and recommended that Judge James S. McAuliffe Jr. sentence him to no more than 25 years in prison for the theft and six child abuse offenses to which he pleaded guilty, according to Janice Stiers, spokeswoman for the state's attorney's office.

The felony theft charge stemmed from the disappearance of more than $6,000 in ski trip money entrusted by youngsters to a travel agency that Harrington operated.

Each of the seven crimes carries a maximum 15-year prison term. Harrington would have faced a possible 105-year sentence if tried and convicted.

Judge McAuliffe consented to the plea bargain yesterday and scheduled a sentencing hearing for Nov. 12, Stiers said.

Harrington's lawyer, Robert Morin, stressed in an interview that McAuliffe agreed to a maximum sentence of 25 years, but could impose a lesser sentence after the Nov. 12 hearing.

On April 2 and April 30 this year, Stiers said, a county grand jury issued six indictments against Harrington, each charging him with one count of child abuse and some charging him with additional sex offenses. As part of the plea bargain, Harrington pleaded guilty to the child abuse charge in each indictment and the state agreed to dismiss the additional, lesser charges at the time of his sentencing.

Stiers said the sex offenses involved boys whom Harrington met through the Big Brothers program or friends of the boys. She said none of the crimes involved students at the high school of the Hebrew Academy of Greater Washington in Silver Spring, where Harrington was principal from 1980 until March 9.

Harrington was honored by President Reagan at a White House reception in December after being named Montgomery County Big Brother of the Year for 1986.

He was being held without bond at the Montgomery County Detention Center last night, awaiting sentencing.

Harrington, 43, was arrested Feb. 28 at his Germantown home and accused of molesting a 14-year-old boy whom he allegedly met through the Big Brothers program. Harrington disappeared two days later after being released on $10,000 bond. By March 6, he had been charged with three additional counts of child sexual abuse, and police were still unable to find him.

For five weeks Harrington eluded authorities, fleeing to New York, Vermont, Rhode Island, the Bahamas and finally to Puerto Rico where, he later told police, he had squandered $16,000 in gambling.

Before he fled this area, he had emptied his bank account, police said.

On April 8, Harrington, after telephoning police about surrendering, stepped off a Metro train at the Silver Spring station and into police custody.

At the time of his surrender, Harrington told police that he was broke and wanted to get help.

During his disappearance, police learned that in 1970 Harrington had faked his own drowning in Vermont the day before he was scheduled to take a polygraph test in connection with a child molestation case there. For 17 years, even his parents believed that he had died in the fake boating accident. Not until they learned of his March arrest in Germantown, and his subsequent disappearance, did they know their son was alive.