BERLIN — American intelligence services monitored former Chancellor Gerhard Schröder beginning in 2002 and perhaps earlier, a leading German newspaper reported on Tuesday. Mr. Schröder, a Social Democrat, openly opposed the Bush administration’s developing plans to go to war in Iraq.

The newspaper, Süddeutsche Zeitung, said its information came from documents and from well-informed United States sources, both in government and in intelligence circles. One source, who like the others was not identified, was quoted as saying the monitoring began because “we had reason to assume that he was not contributing to the success of the alliance.”

The report said Mr. Schröder appeared “at the latest in 2002” as No. 388 on the list of targets for monitoring.

The newspaper quoted Mr. Schröder, who was chancellor from 1998 to 2005, as reacting to the report in a short statement: “Back then, I would not have come to the idea of being monitored by the American intelligence services; now it no longer surprises me.”