WASHINGTON — The long-awaited obstruction-of-justice trial of I. Lewis Libby Jr., who served as Vice President Cheney’s chief of staff, opened with the defense suggesting that the prosecution is an outgrowth of an effort in the White House to protect President Bush’s top political adviser, Karl Rove.

“Karl Rove was the president’s right-hand man. … He had to be protected,” Mr. Libby’s lead defense counsel, Theodore Wells Jr., told the jurors. “Protect Karl Rove. Sacrifice Scooter Libby.”

To bolster the startling argument, Mr. Wells quoted from a note Mr. Cheney wrote in 2003 indicating that he shared the view that an effort was afoot to make Mr. Libby a scapegoat.

“Not going to protect one staffer + sacrifice the guy that was asked to stick his neck into the meat grinder because of the incompetence of others,” Mr. Cheney wrote.

Mr. Wells said Mr. Cheney made the note after hearing Mr. Libby’s complaint that the White House press secretary, Scott McClellan, had publicly cleared Mr. Rove of involvement in the leak of the identity of a CIA operative, Valerie Plame, but was reluctant to issue denials on behalf of a longer list of staffers under suspicion, including Mr. Libby.

When Ms. Plame’s name appeared in the press in 2003, fingers were pointed at the White House because her husband, Joseph Wilson IV, had publicly attacked the case President Bush made for going to war in Iraq. Ms. Plame had worked undercover while abroad, and some of her former colleagues insisted she and her sources were endangered by the disclosure. After an initial inquiry by the FBI, a special prosecutor, Patrick Fitzgerald, was brought in.

Investigators established early on that the leak that led to the first publication of Ms. Plame¹s identity, in a July 2003 syndicated column by Robert Novak, came from the deputy secretary of state at the time, Richard Armitage. It later emerged that Mr. Rove confirmed the fact for Mr. Novak and failed to mention to law enforcement a similar discussion with a Time Magazine reporter, Matthew Cooper. Neither Mr. Armitage, nor Mr. Rove, nor anyone else was ever charged with leaking classified information.

However, in October 2005, Mr. Fitzgerald obtained an indictment charging Mr. Libby with obstruction of justice, two counts of perjury, and two counts of making false statements to the FBI. The indictment alleges that Mr. Libby deliberately lied about his conversations with three journalists who said they talked with him about Ms. Plame, a former New York Times reporter, Judith Miller; NBC¹s Washington bureau chief, Timothy Russert, and Mr. Cooper.

The other major courtroom surprise yesterday was the disclosure that a former White House press secretary, Ari Fleischer, initially declined to cooperate with the probe, citing his Fifth Amendment right not to incriminate himself. After obtaining immunity from prosecution, Mr. Fleischer allegedly told investigators that he told reporters about Ms. Plame’s CIA affiliation. That would make him the third senior administration official to acknowledge disclosing or confirming Ms. Plame’s identity.

“Ari Fleischer had conversations with reporters about Ambassador Wilson’s wife he shouldn’t have had,” Mr. Fitzgerald said yesterday. He said the disclosures could be traced to a “seed” Mr. Libby planted by mentioning Ms. Plame to Mr. Fleischer during a lunch conversation.

Mr. Wells said one of the reporters Mr. Fleischer talked to about Ms. Plame was an NBC News White House correspondent, David Gregory. The defense attorney said the conversation, which took place during a presidential trip to Africa, took place immediately after Mr. Fleischer discussed Ms. Plame with the White House’s communications director, Daniel Bartlett, and was more likely triggered by Mr. Bartlett than by Mr. Libby.

It has long been an open secret that Mr. Cheney’s office was at odds with the State Department and the CIA, particularly over the war in Iraq. Indeed, Mr. Wells said the reference in the vice president’s note to the “incompetence of others” was directed at the CIA’s vetting of the Iraq language in the president’s 2003 State of the Union message. However, yesterday’s disclosures emphasized that the rifts related to the war extended into the White House complex and that the vice president’s office was at loggerheads with Mr. Bush’s political aides over Iraq, at a minimum.

Another indication of divisions within the White House came when Mr. Wells confirmed that President Bush secretly declassified of portions of a key intelligence report on Iraq so the findings could be leaked to selected members of the press. The defense attorney said Mr. Libby was ordered by Mr. Cheney not to discuss the circumstances or fact of the unusual secret declassification with anyone, including the president’s deputy national security adviser at the time, Stephen Hadley. Aside from the finger-pointing at Mr. Rove and the disclosures about Mr. Fleischer, the remainder of the opening arguments of Messrs. Wells and Fitzgerald went largely as anticipated.

“The defendant lied. He made up a story,” Mr. Fitzgerald told the jurors. He did not explicitly ascribe motive to Mr. Libby, but suggested he was nervous about losing his job since Mr. McClellan had said Mr. Bush would fire anyone involved in the leak. He said Mr. Libby stuck by his story that he thought he learned of Ms. Plame from Mr. Russert because changing it would have caused even more trouble. “After this first FBI interview, the defendant planted his feet and was stuck,” Mr. Fitzgerald said.

Since the defense had telegraphed that Mr. Libby would assert that he may have misremembered the conversations with the journalists due to his preoccupation with terror threats and other duties, Mr. Fitzgerald countered that argument by suggesting that the issues surrounding Mr. Wilson were so momentous that the vice president’s aide could not plausibly have forgotten that he learned about Ms. Plame’s identity from official sources and not from journalists.

“It was an issue that could not have been more important. It was someone being accused about lying on the justification for war,” Mr. Fitzgerald said. “The vice president wasn’t going to take it lying down and nor was the defendant….Day after day after day after day, he focused on this controversy.”

Mr. Wells acknowledged that his client was concerned about Mr. Wilson’s charges, but said Mr. Libby viewed as trivia the issue of whether his wife worked at the CIA.

“I speak for Scooter Libby and she was not a big deal to him,” Mr. Wells said. “In real time it was like a sliver. Like a piece of gossip.”

The defense may have gotten some help this argument from the prosecution’s first witness, a former undersecretary of state for political affairs, Marc Grossman. In 2003, he inquired, at Mr. Libby’s urging, how Mr. Wilson, a former ambassador, was assigned by the CIA to travel to Africa to investigate claims that Iraq sought uranium there. He told Mr. Libby how the trip came about, but later made a point of pulling Mr. Libby aside at a White House meeting and telling him that Mr. Wilson’s wife worked at the CIA.

On cross-examination, Mr. Grossman said he saw the issue as not particularly significant at the time. “I thought the whole business was of less than zero importance. I thought the wife was an interesting tidbit, if you will,” he said.

While the defense argued that Mr. Libby may have failed to recall some of his conversations accurately, Mr. Wells also made clear that he plans to challenge the accuracy of the testimony journalists are expected to offer in the case. He suggested that Mr. Russert, who claims to have never discussed Ms. Plame with Mr. Libby, may have been privy to information about Ms. Plame relayed from Mr. Gregory and another NBC reporter, Andrea Mitchell. Mr. Wells said that Ms. Miller has described her recollection of the events as “fuzzy” and that Mr. Cooper’s claim that Mr. Libby confirmed Ms. Plame’s CIA connection is not reflected in Mr. Cooper’s notes.

Mr. Wells’s effort to direct blame at Mr. Rove seemed intended to appeal to a jury that likely leans to the left, since it is drawn from the overwhelmingly Democratic population of Washington. While one of the key defense witnesses, Mr. Cheney, is among the least popular figures in American politics, Mr. Rove is detested perhaps even more strongly by many partisan Democrats. The defense attorney may be hoping that one or more jurors will be disinclined to participate in what could be seen as part of a cover-up to protect Mr. Rove. “I have absolutely no comment,” an attorney for Mr. Rove, Robert Luskin, said yesterday in response to a reporter’s questions about the strategy undertaken by Mr. Libby’s defense.

Mr. Rove does appear on the defense’s witness list. However, that is not a clear indication he will be called, as the defense has indicated it placed some individuals on the list in case unexpected developments required their presence.