WASHINGTON - Today marks the 40th anniversary of the signing of the federal Freedom of Information Act, but open-government advocates say there is little to celebrate.

The historic law is widely seen as broken. The backlog of requests is growing, with some Americans waiting years for information from government agencies.

Each administration since 1966 has used every tool at its disposal to thwart disclosure of information that it deems dangerous or embarrassing. The Bush administration is no different, often citing the changed security environment after the Sept. 11, 2001, terrorist attacks as justification for secrecy.

"The marching orders are now: If there's a basis to withhold, do it," said Elizabeth Withnell, chief counsel at the Department of Homeland Security's Privacy Office.

The law, commonly known as FOIA, presumes that federal records will generally be available to the public. But Congress gave agencies nine broad exemptions they could use to withhold records from the public, including the press.

An analysis of annual FOIA reports from 13 Cabinet-level departments shows that between 2000 and 2004, fully granted FOIA requests fell by 27 percent.

Increasingly, agencies are relying on one of several "executive privilege" claims to deny the release of data and documents.

Open-government advocates say agencies are now using creative interpretations of the FOIA exemptions to conceal as much information as possible.