The Federal Bureau of Investigation is bursting at the seams and urgently needs a new Washington headquarters, a watchdog report says.

The J. Edgar Hoover Building, which occupies an entire block at a Pennsylvania Avenue intersection in downtown Washington, is “aging” and “deteriorating” and needs serious repairs, the Government Accountability Office said Tuesday. The FBI, in coordination with the General Services Administration — which oversees most federal buildings — is reviewing proposals to either renovate the building or move the agency, but none of the options is cheap, the report says.

Much of the problem stems from the agency’s growth since the Sept. 11, 2001, terrorist attacks. Back then, 9,700 headquarters staffers worked at seven locations; now, about 17,300 employees and contractors work at 40 sites across the country, including 22 in the Washington area.

“The FBI cannot afford to continue the status quo,” FBI Assistant Deputy Director T.J. Harrington said in the report, adding later that “a new consolidated FBI headquarters facility is urgently needed, and we view this as one of our highest priorities for the foreseeable future.”

The report and FBI officials agree that there are long-standing security concerns with the agency’s current headquarters and nearby leased locations. The Hoover Building, completed in 1974, is surrounded by four busy roads — Ninth, 10th and E streets and Pennsylvania Avenue. Vehicle barriers and a dry moat guard the building against potential attacks. Still, the Hoover Building is just a few feet from the road.

Much of the agency’s leased annex space is in multi-tenant buildings, and the FBI maintains little control over common areas, including lobbies or parking garages, the GAO said.

So what can the FBI do to find more space? The report suggests several options:

● Stay in the current location. But staying put doesn’t solve space or security concerns, the GAO said, and would require the FBI to continue leasing space. The cost of staying put and renewing leases is expected to climb in the coming years, the GAO said.

● Renovate the Hoover Building and consolidate leases. This option wouldn’t completely solve the space and security problems, but renovations would make the building more energy efficient and allow for the reorganization of floor plans. Renovating and temporarily relocating workers could take up to 14 years and cost at least $1.7 billion, the GAO said.

● Demolish the Hoover Building and rebuild at the same site. Security concerns would remain, but tearing down the building and constructing a new one would solve the space concerns. Agency operations would probably remain dispersed across dozens of locations, the GAO said. Estimates suggest it would take at least nine years and $850 million to complete the project.

● Build a new headquarters at a new location. This option would solve space and security concerns. The FBI said it ideally would find a 50-acre site near Washington area public transportation systems, the GAO said. Last year, the FBI and the GSA estimated that the project would take at least seven years and cost at least $1.2 billion — but the estimates didn’t include costs of new furniture and equipment.

If history is any guide, it could take the FBI more than a decade to find a new home. Congress authorized construction of a new headquarters in 1962, but workers didn’t finish moving into what became the Hoover Building until the late 1970s.

Until the FBI finds a new home, the GAO said the agency should work with the GSA to ensure at least minimal renovations to the current site. Officials quoted in the report agreed with the recommendations.