WASHINGTON — President Barack Obama's new standards for government openness have not trickled down to some agencies, where officials have used special statutes slipped into bills to skirt the Freedom of Information Act, open government advocates said Wednesday.

Efforts to strengthen the 42-year-old law "have been hampered by the increasing use of legislative exemptions that are often sneaked into legislation without debate or public scrutiny," Senate Judiciary Committee Chairman Patrick Leahy said.

News organizations and media groups said new legislation was needed to limit the information agencies may keep secret and for how long...