Now, however, ABC is taking a further look into information Mr. Debat provided. Mr. Ross said ABC had dispatched an investigator to Pakistan to go over details of reports in which Mr. Debat provided information. At the same time, The Associated Press reported last night that it also was investigating three news reports that relied on Mr. Debat for information.

The renewed scrutiny has been driven by revelations about Mr. Debat after a French news Web site, Rue 89, reported this week that an interview supposedly with Senator Obama was entirely made up. Mr. Debat, who could not be reached last night, sent an e-mail message to ABC yesterday saying the allegations against him “are slanderous.”

He told The Washington Post Wednesday that an intermediary had spoken with Mr. Obama. But representatives for Mr. Obama denied that he spoke with anyone connected to Mr. Debat.

Subsequently, other figures whose interviews appeared under Mr. Debat’s byline in the French magazine Politique Internationale have come forward to say they never spoke to him. These included Mr. Clinton; Mayor Michael R. Bloomberg; Alan Greenspan, the former Federal Reserve chairman; Bill Gates, the chairman of Microsoft; and House Speaker Nancy Pelosi.

After his departure from ABC News in June, Mr. Debat continued to work as a senior fellow for national security and terrorism at the Nixon Center in Washington until he resigned his post late Wednesday. He was quoted as a knowledgeable source in an article in the The Sunday Times this month, saying that American military forces were planning attacks that would demolish “the entire Iranian military.” He has also been quoted by many newspapers and news services.