PORTSMOUTH, N.H. ? In twin speeches seen as the unofficial opening of his re-election campaign, President Bush forcefully invoked the memory of the terrorist attacks on New York and Washington, warning Thursday that “America must not forget the lessons of Sept. 11.”

“After all the progress we have made against terror, there is a temptation to think the danger has passed. The danger hasn’t passed, ” Bush told about 1,500 Air National Guard and other service members and families at Pease Air Force Base in this port town. They responded with rousing cheers.

Speaking six months after American forces seized control of downtown Baghdad, Bush vigorously defended his decision to intervene in Iraq, adopting a combative tone against those who question the wisdom of going to war.

“I was not about to leave the security of the American people in the hands of a madman,” Bush said. “I was not about to stand by and wait and trust in the sanity and restraint of Saddam Hussein.”

Presidential politics were clearly on Bush’s mind as he spoke at the air base and then delivered a nearly identical speech to about 600 business and community leaders in Manchester, N.H.

Although New Hampshire is a staunchly Republican state, Bush won it by a narrow margin in 2000. Its January primary date — second on the presidential calendar — has brought Democratic candidates to the state, using it as their main stage to condemn the president and his policies.

In his remarks, Bush spoke with vigor, using a revamped stump speech that mixed well-worn applause lines with new, more forceful language — especially on Iraq.

“Wars are won on the offensive,” Bush said. “And our friends and America are staying on the offensive.”

Bush provided a list of American achievements in Iraq: schools rebuilt, hospitals reopened, children immunized, water and electricity restored.

Bush said that last week’s report by weapons inspector David Kay confirmed what his administration had consistently claimed — “that Saddam Hussein was a deceiver and a danger.”