Obama outlined his benchmarks for making any new decision about troops there: whether al-Qaida and other terrorist groups can set up safe havens in Afghanistan, whether the Afghan national army and police can secure the country without assistance, and whether the border with Pakistan can be made less porous.

"We can't tolerate a situation in which terrorist organizations act with impunity," he said.

Minutes before his vice president, Joe Biden, landed in Iraq for a two-day visit, Obama said he was confident — but not certain — that the timetables for removing U.S. troops from that war will hold. This week marked a major milestone in the war when U.S. troops pulled out of major Iraqi cities.

"I reserve the right to make changes based on changing circumstances to protect U.S. security," he said.

As for Guantanamo detainees, the former constitutional law teacher expressed doubts about his call to create a new legal framework to deal with terror suspects considered too dangerous to release but also impossible to prosecute, a potential major change in American jurisprudence.

"We're going to proceed very carefully on this front, and it may turn out that after looking at all the dimensions of this that I don't feel comfortable with the proposals," Obama said. "We don't have a tradition of detaining people without trial."

He added: "How we deal with those situations is going to be one of the biggest challenges of my administration."

Obama predicted that "a sizable number of" the suspected terrorists and foreign fighters now being held without charges at the prison in Cuba would get their day in court, either in civilian federal courts or military tribunals.

With prospects for congressional approval of "prolonged detention" murky, there has been talk that the White House might simply declare changes to be in effect.

"I am not comfortable with doing something this significant through executive order," Obama said.

The president spoke sympathetically at one point of the white firefighters in New Haven, Conn., who said they had been discriminated against and won their case this week before the Supreme Court.

He added that both the damage and benefits of affirmative action are overstated, saying that racial preferences in hiring or admissions could become "an afterthought" if problems such as malnutrition, poverty and substandard schools could be eliminated, creating a more level playing field among whites and minorities.

"I've always believed that affirmative action was less of an issue, or should be less of an issue, than it's made out to be," Obama said.

With joblessness rising, the president said he was "deeply concerned" that too many families are worried about "whether they will be next."

New government figures out Thursday showed the unemployment rate grew to 9.5 percent last month, and economists agree it is likely to rise into the double digits. Since Obama signed the $780 billion economic stimulus bill in February, the economy has shed more than 2 million jobs.

"What we are still seeing is too many jobs lost," said Obama.