WASHINGTON – A top assistant to the White House deputy chief of staff, Karl Rove, appeared last week before the federal grand jury investigating possible criminal wrongdoing by the Bush administration in the exposing of a CIA operative, a person familiar with the case said Tuesday.

The interest in Susan Ralston, Mr. Rove’s longtime executive assistant, was unclear; but it comes as special prosecutor Patrick J. Fitzgerald has been focusing on differences in witness statements made to federal agents and the grand jury investigating who revealed the identity of Valerie Plame.

Ms. Ralston’s appearance Friday followed grand-jury testimony last month by a Time magazine reporter, Matthew Cooper, who recounted a conversation he had with Mr. Rove in July 2003 in which Rove alluded to Ms. Plame without mentioning her by name. Mr. Cooper and columnist Robert Novak subsequently wrote stories identifying Plame after talking with administration officials.

It can be a violation of federal law to disclose the name of a covert CIA agent. Some people close to the case have said they believe Mr. Fitzgerald has begun focusing on whether other laws may have been broken, such as perjury, obstruction of justice, or making “misstatements” to investigators.

Mr. Cooper’s version of his conversation with Mr. Rove differed from the version Mr. Rove has offered investigators. Some people close to the case said Mr. Fitzgerald apparently was seeking to resolve the differences in the two stories.

A person familiar with Mr. Cooper’s testimony said Ms. Ralston’s name did not come up during the reporter’s grand-jury appearance. That indicates Mr. Fitzgerald may be interested in her testimony for other reasons.

Ms. Ralston could not be reached for comment.

The prosecutor earlier said in court papers that his investigation essentially was complete as of last October except for the testimony of Mr. Cooper and New York Times reporter Judith Miller. Ms. Miller was jailed four weeks ago for refusing to cooperate and remains incarcerated.

ABC News, which first disclosed Ms. Ralston’s grand-jury appearance, reported that former Rove aide Israel “Izzy” Hernandez appeared before the grand jury Friday.

Mr. Hernandez is a longtime aide to President Bush who once worked as a travel assistant for Mr. Bush during his run for governor of Texas in 1994. More recently, he was a deputy to Mr. Rove until being nominated earlier this year to be an assistant secretary of commerce.

A Commerce Department spokeswoman declined to comment.

Mr. Fitzgerald, who has been leading the investigation since December 2003, has not indicated when he intends to be done. The grand jury that has been hearing testimony is set to expire in October, although it could be renewed.

Robert Luskin, Mr. Rove’s attorney, declined to comment about Ms. Ralston’s appearance. He has said repeatedly that Mr. Rove has been assured he is not a target of the investigation, and that investigators have never challenged the veracity of any statements Mr. Rove has made to them over the course of the investigation.