The District of Columbia government has prepared plans for a top-to-bottom, $20.9 million renovation of the 78-year-old District Building, including construction of a new City Council chamber in the building's courtyard and an exercise room in the basement.

The National Capital Planning Commission is expected to consider the city's renovation proposal at its April 3 meeting. Commission staff members said they had not yet examined the voluminous reports prepared by the architectural firm of Devrouax & Purnell, the city's consultant on the project.

City officials said that Mayor Marion Barry's recent diversion of $5.2 million from the fund set aside for the first phase of the renovation may delay the project. Last month, Barry diverted that money to complete construction of the new municipal center at 14th and U streets NW.

Renovation of the neoclassic marble building would include reopening the front doors, which have been closed for several years, building two new stairwells to ease escape from the building in case of a fire, installing new heating and air-conditioning systems, replacing the roof that city records say has not been improved in generations, putting in new windows, restoring historic detailing such as the marble facades and making a variety of other alterations.

The Devrouax firm's report raised special concerns about ways in which the District Building's layout makes it vulnerable to terrorist attack, and about what it said was the laxity of the security guard staff in checking the bags of visitors.

"Security hazards of an extreme and dangerous nature exist due to the ineffectiveness of examinations conducted on the belongings of building visitors," said the report.

"This project is long overdue," said council member Betty Ann Kane (D-At Large). "There are real safety and security problems that have to be corrected. It's a fire hazard."

Kane and others cited the fact that the building has only one set of stairwells, and no fire escapes.

The consultant's report said that the problem-prone building must be made "worthy of being the seat of the local government."

It added that the renovation was in line with the sprucing up of other parts of Pennsylvania Avenue. The District building is at 14th Street NW and the avenue.

Parts of the proposal must be approved by the City Council. City officials said that because of the delays it is impossible to say when construction will begin.

Funds for part of the project have been included in the city's capital budget since 1982. City workers in the building welcomed the proposal as their best hope for relief from the cramped, often leaky, drafty quarters.

"The heating system is crazy," said one council staff member who did not want to be identified. "The maintenance problems are becoming so clear."

She said that partitions divide her council member's office into numerous rooms, but heat is provided in only two of the rooms, so most employes are cold in the winter.

"It's a very old building," said Cyril Crandon, the D.C. Public Works Department official overseeing the project, "and it needs a lot of mechanical and structural improvements."

The new council chamber, planned for the the courtyard of the U-shaped building, would have 8,000 square feet, almost three times the size of the current one on the fifth floor, which is 3,000 square feet.

The current chamber seats 122 in the audience, and the new one would have 300 seats, some in a second floor gallery.

The consultant's report was extremely critical of the city security staff.

"Of greatest concern is the fact that 'no one is in charge' during emergencies," the report said.

In addition, the guards "cannot effectively control" people entering the building, the consultant said.

A "major concern" is employes who disregard security regulations. The report said, for example, that guards have found more city employes entering the building with concealed guns than members of the public.

To discourage a terrorist attack, the report recommended surveillance equipment, electronic gates, entrance barriers, secure areas, a security command post and measures to limit access to the mayor's fifth floor office.