WASHINGTON - President Barack Obama will place the threat posed by radicalized, homegrown extremists at the center of his new national security strategy, his top counter-terrorism aide said Wednesday.

Obama will also de-emphasize the "war on terror" concept favored by the former Bush administration, which drove US foreign policy for years after the September 11 attacks of 2001, when he releases the strategy on Thursday.

Following a spate of attacks or near misses - at Fort Hood military base last year and in Times Square, New York, this month - the administration appears to have reframed the matrix of threats to US national security.

"We've seen an increasing number of individuals here in the United States become captivated by extremist activities or causes," said John Brennan, deputy national security advisor for counter-terrorism and homeland security.

"The president's national security strategy explicitly recognizes the threat to the United States posed by individuals radicalized here at home," Brennan said at the Center for Strategic and International Studies.

"We've seen individuals, including US citizens, armed with their US passport, travel easily to terrorist safe havens and return to America, their deadly plans disrupted by coordinated intelligence and law enforcement."

Faisal Shahzad, the top suspect in the failed car bombing in Times Square on May 1, is a naturalized US citizen, who allegedly became radicalized after years in the United States and received training by Pakistani extremists.

Major Nidal Hasan, an American-born army psychiatrist who is the only suspect in the killing of 13 people at Fort Hood army base last year, was allegedly drawn to radical thought while serving in the armed forces.

Brennan said that "unprecedented" pressure ratcheted on Al-Qaeda since Obama took office has severely limited the group's ability to move, raise funds, recruit and carry out attacks.

But he said the network was now relying on poorly trained "foot soldiers" who might be able to slip past US defenses because they do not fit the conventional profile of a terrorist.

"This is the new phase of the terrorist threat, no longer limited to coordinated, sophisticated, 9/11 style attacks," Brennan said.

"As our enemy adapts and evolves their tactics, so must we constantly adapt and evolve ours, not in a rush driven by fear, but in a thoughtful and reasoned way that enhances our security and further delegitimizes the actions of our enemy."

Brennan also appeared to deliver the White House's most explicit rejection yet of "war on terror" terminology in defining its thinking about the problem.

"The president's strategy is absolutely clear about the threat we face. Our enemy is not terrorism because terrorism is but a tactic.

"Our enemy is not terror because terror is a state of mind and, as Americans, we refuse to live in fear.

"Nor do we describe our enemy as jihadists or Islamists because jihad is holy struggle, a legitimate tenet of Islam meaning to purify oneself or one's community."

Brennan said that Obama had a single-minded focus on his goal to disrupt, dismantle and destroy Al-Qaeda.

In his last national security strategy in 2006, ex-president George W. Bush targeted terrorism as a concept much more specifically, declaring boldly "the war on terror is not over."

Brennan said that Obama envisaged using the full arsenal of diplomatic, military, developmental, law enforcement, intelligence and homeland security powers available to a US president.

"This strategy aims to renew American leadership in the 21st century by rebuilding the fundamental sources of American strength, security, prosperity and influence in the world." he said.