The Manassas City Council has informally approved the concept of a four-story city hall with the option of building a fifth floor later if necessary, according to City Manager Macon Sammons. The design firm of Architect Associates has been instructed to proceed with the design work while the council debates whether the city's social services offices should be housed in the new building or remain on Center Street, he said. The new building will be located where the city hall annex is now, Sammons said, and the old city hall will be used for a museum. The new building, which has a 1985 budget of $1.4 million, is scheduled for completion by January 1987. It may cost up to $3 million, according to John Grzejka, finance administrative assistant.

Bids for the second phase of renovation for Osborne High School in Manassas are expected to be received by school Superintendent Brent Sandidge by early next month, he said. Bids for the renovation could total between $500,000 and $750,000. Sandidge said the school's new science wing is slated for completion by December 1985 at a cost of $7.5 million.

Manassas resident Karen McClellan will be among the dancers performing "The Nutcracker" when the Virginia Ballet Company and School presents the Tchaikovsky ballet today, tomorrow, Saturday and Sunday. Tickets for the show, to be held at Woodson High School, 9525 Main St., Fairfax, cost $4, $6 and $8. For more information and reservations call 321-8009, 321-8013 or, after 7 p.m., 451-2425.