WASHINGTON – The Obama administration said Wednesday it has alerted Congress and begun notifying foreign governments that the WikiLeaks website is preparing to release sensitive U.S. diplomatic files that could damage U.S. relations with friends and allies.

Officials said the documents may contain everything from accounts of compromising conversations with political dissidents and friendly politicians to disclosures of activities that could result in the expulsion of U.S. diplomats from foreign postings.

U.S. diplomatic outposts have begun notifying other governments that WikiLeaks may release the documents soon.

“These revelations are harmful to the United States and our interests,” State Department spokesman P.J. Crowley said. “They are going to create tension in relationships between our diplomats and our friends around the world.”

Crowley said the public airing of what were supposed to be private communications will likely erode trust in the U.S. as a diplomatic partner. And he said they could cause embarrassment if the files include derogatory or critical comments about friendly foreign leaders.

“When this confidence is betrayed and ends up on the front pages of newspapers or lead stories on television or radio, it has an impact,” Crowley said.

The release is expected this weekend, although WikiLeaks has not been specific about the timing.

Officials speaking on condition of anonymity to discuss sensitive internal matters said the administration believes that the diplomatic fallout could be substantial. Many of the cables are believed to date from the start of the Obama administration, meaning that the White House won’t be able to distance itself from any disclosures.

U.S. officials are concerned that some of the leaked cables could include details of conversations in which senior foreign politicians offer candid appraisals of their governments. Those assessments could prove embarassing, not only to the United States but to the politicians and governments concerned.

Some of the documents may provide specifics of meetings U.S. diplomats have had with opposition leaders, dissidents or human rights activists in various countries that could expose them to retaliation, particularly in authoritarian nations, officials said.

A key focus of the documents is Europe, but the cables are likely to touch on relations with many key countries in Asia and elsewhere, another official said.