WASHINGTON — Top intelligence and law enforcement officials will meet on Thursday with Republican congressional leaders to share highly classified information related to an F.B.I. informant who contacted members of the Trump campaign in the early days of the Russia investigation, a White House official said on Tuesday.

But even those few details prompted confusion around Washington, with a Justice Department official refusing to confirm the White House’s announced guest list and Democrats on Capitol Hill complaining they were not invited.

The meeting promised to be a flash point in the standoff pitting President Trump and his congressional allies against his own administration’s top law enforcement officials.

At the root of the dispute is a subpoena by Representative Devin Nunes, Republican of California and the House Intelligence Committee chairman, for all documents referencing or related to the informant, an American academic who met on behalf of the F.B.I. with Trump associates.