Within 60 days, four Washington developers will start a five-story, 125,000 square foot private office building on an acre-plus urban renewal site in the heart of Old Town Alexandria.

The reddish-brown brick office building, facing King Street, will be built on air rights to be purchased from the city for $235,000 by developers Donald Brown, Lawrence Brandt, Joseph Gildenhorn and Benjamin Jacobs. (That group had previously held a contract on the urban renewal site and had plans to build a condominium apartment there. However, the city decided to buy it as a site for a new court house and to sell air rights to the developers for an office building.)

Brandt also heads a construction firm that will build the $6.5 million office building.

Saunders, Cheng, Appleton & Associates, an Alexandria architectural firm, designed the office building to be built over the underground parking structure (300 spaces on four half levels) now being constructed by the city on the site that also is bounded on the east and west by S. Pitt and St. Asaph streets and an alley to the south.

The same architectural firm also has designed the four-story court house that Alexandria will build in back of the new office building. That structure is expected to be started in June.

Plans call for the court house to be entered via a two-story arcade on King Street in the center of the office building. Inside the office building and in front of the new court house itself will be an inner courtyard. Commercial space will be developed on the first floor of the new office building that will be topped by a mansard roof with colonial windows.

Incidentally, the same partnership of Washington developers earlier did a small office building farther east on King Street and also the nearby Old Town Holiday Inn at the southeast corner of King and Pitt.

Brandt and the same partners also have completed 46 traditional townhouses on Princess Street in Old Town and plan to begin 46 more on Oronoco Street. Prices of the original townhouses ranged up to $179,000.

Additionally, Brown, Gildenhorn and Jacobs also have started excavation work for a 10-story, 93-unit condominium apartment building on the north side of the 2100-block of P Street NW, which had been a parking lot. Omni Construction will be the builder.

The same devlopment group, along with a subsidiary of the Louis Dreyfus Holding Co. of Paris, is currently completing a hotel-office complex at 2800 Pennsylvania Ave. NW. The 218-room hotel, scheduled to open this summer and to be operated as a Four Seasons franchise, will offer rooms and services at the city's highest level.

Brown, Gildenhorn and Jacobs, who have been partners as attorneys and as real estate developers for 10 years, occupy office space in a building that they completed two years ago at 1220 19th St. NW. They also have a real estate management firm, JBG Properties, headed by Joseph Seubert. Management contracts involve aproximately 8,000 apartment units located in nearby areas and also in Pennsylvania, Massachusetts, Louisiana, Alabama, Florida and Mississippi. King's Row

The King Organization, a firm that has specialized in low-moderate-priced condominium town houses and garden apartments in Northern Virginia for more than a decade, plans a March start on a grouping of 10 all-brick town houses in what now is regarded as a less than trendy area of intown Alexandria.

Ludlow (Pete) King III, a former Marine helcipoter pilot in Vietnam and president of the firm since 1974, said this week that a one-third-acre vacant site at Patrick and Pendleton streets will be developed with three-story dwellings that will have 1,700 square feet of living area, including garages. Three of the houses will face Pendleton Street and the other seven will back on Patrick (U.S. 1 north) and be located inside a seven-foot brick wall. Prices are expected to be in the $110,000 range.

"It's an area, sometimes called Old Town West, which has older houses, public housing and light industrial areas," said King."In fact, we're right next to a lot used to park you-haul-it trailers. But we see this as an area on the way up. It's only half a dozen blocks from the heart of this charming old city and it's only four blocks from the new Metro blue line (Braddock Road) station."

Metro now is being extended south of National Airport to Huntington. The Braddock Road station is expected to be open in two years.

King, 36, said that his father (Ludlow King II, also known as Pete) found the site and negotiated the purchase from Fireside Investors. A graduate of West Point and a former trade association executive, the senior King founded and headed the firm for a number of years. He recently decided to come out of a retirement that he undertook voluntarily two years ago. "I really missed being a part of building," he said earlier this week.

Lewis, Wisnewski & Associates of Alexandria designed the King's Row town houses to have detailed colonial brickwork. The dwellings are expected to be completed late in 1979.

A pioneer firm in offering lowerpriced condominium dwellings in varied parts of Fairfax County since the late 1960s, the King group recently has been building condominium cluster dwellings and fee simple town houses in the Gunston Road area near Rte. 1.

"Instead of looking for large tracts of ground on which to develop many houses over a period of years, we now are looking at smaller, closer-in locations where innovative groupings of fine houses can be built to attract both the younger and older affluent markets," said the junior King. "We'd like to do more building in Alexandria because we know there's a market there."

Several years ago other developers began expensive rehabilitations and small group of new townhouses just west of Washington Street and within two or three blocks of King Street. However, the King's Row town house cluster will be the first expensive town houses near Rte. 1 and six blocks north of King Street. However, several nearby older houses have recently been renovated and a few new houses have built and sold on nearby sites.