WASHINGTON  The National Security Agency is facing renewed scrutiny over the extent of its domestic surveillance program, with critics in Congress saying its recent intercepts of the private telephone calls and e-mail messages of Americans are broader than previously acknowledged, current and former officials said.

The agency’s monitoring of domestic e-mail messages, in particular, has posed longstanding legal and logistical difficulties, the officials said.

Since April, when it was disclosed that the intercepts of some private communications of Americans went beyond legal limits in late 2008 and early 2009, several Congressional committees have been investigating. Those inquiries have led to concerns in Congress about the agency’s ability to collect and read domestic e-mail messages of Americans on a widespread basis, officials said. Supporting that conclusion is the account of a former N.S.A. analyst who, in a series of interviews, described being trained in 2005 for a program in which the agency routinely examined large volumes of Americans’ e-mail messages without court warrants. Two intelligence officials confirmed that the program was still in operation.

Both the former analyst’s account and the rising concern among some members of Congress about the N.S.A.’s recent operation are raising fresh questions about the spy agency.