WASHINGTON — Seeking to undercut Senator Clinton’s claim on the centrist mantle of the Democratic presidential primary, Senator Obama is unveiling a hawkish new approach to the battle against terrorism with a vow to strike at Al Qaeda elements in Pakistan unilaterally if its president fails to act. Pledging to “take the fight to the terrorists,” the first-term Illinois senator yesterday called for a more aggressive line against Pakistan and said he would send additional American troops to Afghanistan. At the same time, he stepped up his criticism of the Iraq war, castigating both the Bush administration and his Democratic competitors who authorized it in Congress. Those lawmakers, he said, “rubber-stamped the rush to war” and became its “co-author.”

Mr. Obama, who came out against the war as an Illinois state legislator in 2002, said yesterday that it has undermined American security.

The 35-minute policy address in Washington was striking in its echoes of Clintonian triangulation, as Mr. Obama sought to meld his opposition to the Iraq conflict and a “fresh” approach to diplomacy with a more traditional embrace of America’s military might. He characterized Iraq as the wrong battlefield. He accused President Bush of “fighting the war the terrorists want us to fight” and said America must instead confront terrorists in Afghanistan and Pakistan.

“There must be no safe havens for terrorists who threaten America,” Mr. Obama declared, decrying as a “terrible mistake” the Bush administration’s failure to take out the leadership of Al Qaeda in Pakistan in 2005.

Expressing limited patience with the administration of President Musharraf, Mr. Obama promised that such a lapse would not occur if he becomes president.

“If we had actionable intelligence about high-value terrorist targets and President Musharraf will not act, we will,” he said. Mr. Obama later added: “I will not hesitate to use military force to take out terrorists who pose a direct threat to America.”

Rival campaigns viewed Mr. Obama’s speech as a direct attempt to rebut the perception — fanned by the Clinton campaign over the last week — that his willingness to engage enemy dictators personally showed a glaring foreign policy weakness.

Indeed, the speech’s objective of presenting Mr. Obama as a strong, tough candidate for commander in chief was evident at every turn, from his campaign’s emphasis on his aggressive stance on Pakistan to the senator’s own delivery. Standing behind a podium and using Teleprompters at the Woodrow Wilson International Center for Scholars, Mr. Obama’s tone was forceful; his voice often rose to punctuate the ends of sentences in a departure from the low-key, professorial tone he sometimes adopts to connect with voters on the stump. Mr. Obama drew reactions from just about all of his Democratic opponents, with one notable exception: Mrs. Clinton, whose campaign said nothing at all.

Senator Dodd of Connecticut offered the most stinging criticism, singling out Mr. Obama’s comments on Pakistan. “Frankly, I am not sure what Barack is calling for in his speech this morning,” Mr. Dodd said in a statement. “But it is dangerous and irresponsible to leave even the impression the United States would needlessly and publicly provoke a nuclear power.”

Mr. Dodd said that while he would move against Osama bin Laden and other terrorists, he would not “declare my intentions for specific military action to the media in the context of a political campaign.”

The campaign of Senator Biden of Delaware sent out a statement to “congratulate” Mr. Obama on his “Johnny-come-lately” position, citing a long-standing push by Mr. Biden for more troops and reconstruction aid to Afghanistan and for more cooperation from Pakistan in the war on terrorism. But Mr. Biden, the chairman of the Senate Foreign Relations Committee, also chastised Mr. Obama for being too specific. “The last thing you want to do is telegraph to the folks in Pakistan that we are about to violate their sovereignty,” he said in an appearance at the National Press Club, according to his campaign.

John Edwards of North Carolina and Governor Richardson of New Mexico did not criticize Mr. Obama directly, but issued statements saying that while they would use military force to fight terrorism, their focus would be on diplomacy first.

Mr. Obama earned praise from a Democratic foreign policy heavyweight, Lee Hamilton, who served as vice chairman of the Iraq Study Group. “It is the most comprehensive statement on counterterrorism that I have seen made by a presidential candidate,” he said. A former Indiana congressman, Mr. Hamilton now heads the Wilson Center and introduced Mr. Obama before his speech. He voiced support for Mr. Obama’s challenge to Pakistan, although he is not endorsing the senator’s candidacy. Even as he pledged not to shy away from military force, Mr. Obama reiterated an emphasis on diplomacy, standing by his much-publicized promise last week to meet with rogue leaders without preconditions. In the first direct spat of the campaign, Mrs. Clinton had deemed Mr. Obama “irresponsible” and “naïve,” prompting him to link her to the legacy of the Bush administration.