An unidentified entity is backing a new lawsuit to expose America's secret defense pact with the Emirate of Kuwait.

The suit, filed in federal court in Washington last week by the law firm of Hogan & Hartson, seeks the declassification of a military cooperation agreement that America signed with Kuwait after the Gulf War in 1991 and which it renewed in 2001.

Hogan & Hartson brought the case in its own name and did not disclose the identity of the mystery client pursuing the information. The lawyers who filed the suit, Thomas McGovern III and Steven Williams, did not respond to phone messages seeking comment for this article.

The law firm said it sought the agreement from the Pentagon in May 2006 under the Freedom of Information Act. The Defense Department responded that the pact is entirely classified, but the lawsuit alleges that some part of it should be public, since public officials and a variety of government publications have made statements discussing provisions in the deal.

The suit also claims that "similar agreements" with Egypt, Jordan, and countries in the North Atlantic Treaty Organization are public.

According to a Congressional Research Service report, the deal with the Kuwaitis "is said to provide for joint military exercises," as well as American arms sales to Kuwait and training for Kuwaiti military personnel.

"These agreements were done with a bunch of Gulf states, Kuwait, Qatar, and all of these places" after the Gulf War in 1991, an adjunct professor at the National Defense University, Sami Hajjar, said. "They're very short and very simplistic and have something to do with the pre-positioning of materiel."

Mr. Hajjar said the secrecy is driven by the desire of Kuwait's leaders to minimize the discussion about American involvement in the country. "They don't want to reveal to their people that they have agreements which might detract from their sovereignty," the professor said. "In particular for Muslim extremists, that's where the sensitivity is and is why those things are classified and in my judgment perhaps should continue to be."

Mr. Hajjar said another potential flash point is a so-called status of forces agreement, which reportedly guarantees that American military personnel will be immune from action in Kuwaiti courts.

The Kuwaiti government publicly opposed the invasion of Iraq in 2003, but it closed off 60% of its territory to permit a force of 250,000 American personnel to stage the attack. A 2006 congressional report said the American military has about 10,000 people officially based in Kuwait, though as many as 90,000 are present at any given time as troops rotate in and out of Iraq.

There are hints in the lawsuit that Hogan & Hartson's client may be a company that does business with the American military in Kuwait and is involved in some litigation relating to an accident there. In addition, Mr. McGovern, one of the lawyers who brought the case, is an expert in government contracting law who has written about the legal perils for companies working in hazardous areas like Iraq.

The Embassy of Kuwait in Washington did not reply to an interview request. A spokesman for the Justice Department, Charles Miller, said he had no record of the suit being served on the government yet.

"We classify information we feel could be a threat to the safety of the U.S. government, our soldiers, citizens, or to our allies," a Pentagon spokesman, Lieutenant Colonel Mark Wright, said, stressing that he was speaking in general terms and was not familiar with the Kuwait pact.

An attorney who specializes in Freedom of Information Act cases, Scott Hodes, said the law firm faces an uphill battle in trying to persuade a judge to reverse the Defense Department's position on classification.

"When the only issue is classified information, it's really hard to defeat the government," the former FBI lawyer said. "That's not to say it's impossible, but it's very hard."