Improvements and maintenance of the nation's existing housing stock now total more than $33 billion annually. Our share in the Washington metropolitan area is about $500 million.

That would mean an average of about $500 for each of the area's 1 million units. However, the rehabilition tab on many of the area's older housing units, expecially those undergoing major renovation in the District, would abviously be considerably higher.

One unusual, major rehabilitation of a fairly large intown residence was recently competed by a 24-year-old young man with a real estate tradition in his family. He also had a strong desire to do something significant on his own after breaking into maintenance and upkeep as a "broom handler."

Nearly three years ago, Washington resident William Christopher Smith Jr. got out of Villsnova University with a degree in economics and a chance to join his father's real estate firm here. Much of the firm's activity in recent years has been in the acquisition of rundown apartment dwellings and rehabilitiating them for a return to the market.

"You could say that I learned something about rehabbing by working with our maintenance staff of carpenters, plasterers and painters," Smith said. "Then I found a 60-year-old house at 3718 Woodley Rd. NW. It was originally built to house two families on two floors but I figured it could be bought right for $45,000 and fixed up for about another $45,000 and then be resold for something around $100,000."

That was before Smith got started on the job of redoing and enlarging the house that now, seven months and much hard work later, he had put on the market for $215,000. He obtained financing through some of his father's lending connections.

"Iput a lot of myself into the job and I think it's worth it. The market wil give me my answer," he said.

What did this smiling, tousle-haired young man do to this house that now stands in a new splender between two small apartment huilding?

"After making the decision to almost gut the house and save the plastered walls, I decided that the dwelling would be better for one family. And it seemed to make sense to get rid of old porches on one side and enlarge both living floors with a Tudor styled addition.

"That provided space on the first floor for a den with fireplace, solid oak herringbone floors and oaks paneling with crown and panel molding. On the second floor, where there are now four bedrooms, the extra space was used to make the master bedroom really large with a fireplace and a bath with special Spanish tile."

In terms of his own contribution, besides the visualization of the finished house, Smith also selected all the materials - ceramic tile, the paneling, new windows, brass door sets, door stops and fireplace equipment, the ceramic tile for the kitchen and the solid cherry cabinets, among other items.

He was particularly proud of recognizing the quality of original trim on the doorway and scraping same and William Christopher Smith Jr. has redone replacing it. "I also like the front door so we redid it completely. All the windows were replaced. The original steel casements are now wood with Tudor-styled munitins and shutters. And the glass is double-glazed and isulated.

Some of the charm of the house that Chris Smith rebuilt is in the things he saved - the front door, the woodwark and the classic iron fence in front. He added a two-car garage, landscaping and canvas awning for the patio in back.

Now that he has redone an intown dwelling to his own taste, Chris Smith would like to tackle some new projects in rehabilitiation - restoration field that has become so abundantly active in this area in the past few years.

"But first I'll have to find a buyer for the house on Woodley Road.We showeds the house last weekend and the reaction seemed to be favorable," he said hopefully.

(Fore more Real Estate Happenings, see D10.)