The devastating effects of the terrorist bombing of the Alfred P. Murrah federal building in Oklahoma City in 1995, which claimed 168 lives, prompted new design standards for making government buildings — particularly those housing law enforcement and intelligence agencies — less vulnerable to explosives.

But it was not until a year ago that a subcommittee of the Interagency Security Committee began trying to establish nationwide standards for 150 million square feet that the federal government leases from private building owners. This process has proved challenging because safety measures are costly, whether they involve giving up space so that a building can be set far back from the curb or hiring guards and installing electronic turnstiles to limit access.

Real estate industry representatives have met several times with federal officials during the past year to seek assurance that landlords will not have to foot the additional costs, which they say could make it impractical for them to lease space to government agencies, The New York Times reported.

The General Services Administration (GSA), which oversees federal procurement practices, did not plan to terminate leases in buildings that do not offer deep setbacks or meet other standards.

Complicating matters is the fact that the Federal Protective Service, the security agency for federal tenants, has moved from the GSA to the new Homeland Security Department, adding a layer of bureaucracy.

Some developers say they are incorporating security features into their new buildings as if the standards had already been imposed. Patriots Plaza, a million-square-foot project being developed by Trammell Crow in southwest Washington, is being billed as the first private speculative office complex that was designed specifically to meet post-Sept. 11 security standards. Thomas E. Finan, a Trammell Crow principal based in McLean, Va., said that while the collapse of the twin towers had refocused attention on building security, the engineering principles being applied stem from Oklahoma City because car bombs or other explosives were considered the most likely form of attack.

In Washington, where building height is limited to 12 stories, an airplane attack on an office building is considered unlikely.

In building Patriots Plaza, an effort was made to avoid repeating the mistake made by developers of data centers in the 1990s, who included so many refinements that the owners could never recover their investment.

A structural engineering technique known as "progressive collapse avoidance" is being applied to prevent the kind of pancaking that occurred after the World Trade Center was attacked. Window frames are being designed to accommodate the thickest blast-resistant glass. The entrance to the first building will be 30 feet from the curb, but setbacks for the other two could be expanded to 50 feet, if that is what the government requires. The building will be made of precast concrete reinforced with steel to withstand the pressures of an explosion.

The garages will look as if they are part of the buildings but will actually be separate hardened structures, so that if a bomb goes off underground, the impact will not be felt elsewhere in the building. Similarly, the lobby will be built to be "expendable" in the case of a blast, to confine casualties to that area.

Experts say these and other features had increased construction costs by 8 to 10 percent. But these costs had been offset by the fact that the land costs were low — about $55 a square foot for the first phase, compared with $125 a foot in the East End, the downtown neighborhood east of the White House that has been experiencing a revival after years of neglect. Trammell Crow's equity partner in the project is Multi-Employer Property Trust, one of the country's largest pension plan investment funds.

In an effort to protect occupants from chemical or biological attacks, air intake equipment would be on the roof, as it is in most buildings in New York City. But much less was known about how to prevent death or injury from this type of attack than from an explosion.

As they wait for the new security standards to be announced, building owners and managers already have more than an inkling of what they are likely to entail.

In November 2002, before the decision was made to adopt nationwide guidelines, the GSA drafted standards for Washington and its surrounding suburbs, where the federal government leases about 47.6 million square feet of space. Based on standards that were developed for the Department of Justice, the guidelines divide leases into four categories, depending on the number of employees in the building and the nature of the work being performed, and are more demanding for new construction than for existing buildings.

The strictest standards pertaining to setbacks, blast-resistant windows, and access control for entrances and parking lots would be applied to buildings with more than 450 employees. Classified as Level 4 buildings, they would generally be more than 150,000 square feet in size and likely to house law enforcement and intelligence agencies deemed to be at high risk of attack.

At the opposite end are Level 1 buildings with 10 or fewer employees who have little contact with the public. But a smaller building could fall into the Level 4 category if, for example, space was occupied by a day-care center.

Building owners say they are concerned about who would pay for access control in buildings in which the government is not the only tenant. They say they are also worried about driving away desirable tenants — law firms, in particular — that might be loath to put up with additional layers of security and the possibility that older buildings will no longer be able to attract government tenants.

There is also the question of whether the new standards will tend to favor suburban office parks at the expense of urban buildings, said Roger Platt, a senior vice president of the Real Estate Roundtable, an advocacy organization for the major real estate companies.

An even more ticklish issue is whether the federal government would allow retail uses in buildings housing more sensitive agencies. Store owners, of course, are not likely to subject their customers to security checks. The GSA acknowledged that a blanket ban on retail could cause havoc but said that there might be instances when it would be safest for an agency to be the only tenant in a particular building.