The Alexandria City Council voted 5 to 1 yesterday, with one council member absent, to buy for $1.5 million a choice, one-acre parcel of surplus federal land in the city's booming Old Town section.

The decision settles one part of a four-year-old feud with the General Services Administration over the city's attempt to buy the property. Alexandria recently filed suit in federal court, charging that the government had reneged on an agreed-upon price of $925,000 for the parcel, now a parking lot at 219 N. Lee St. near the city's rapidly developing Potomac riverfront.

The city's complaint charged the GSA with delaying sale of the property for more than two years after the city agreed to buy it in 1979 and paid a $92,500 deposit. During the delay, the property's assessed value rose to $1.5 million, and the city's deposit was returned without interest.

Mayor Charles E. Beatley said yesterday that the purchase agreement allows the city to pursue its litigation to recover the $500,000 difference in price. Vice Mayor James P. Moran cast the sole dissenting vote. "I think we've been treated dishonorably and unlawfully," he said