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President Obama, showered with foreign policy questions at his first press conference of the year, defended his sanctions-heavy approach to Iran's nuclear program and urged the international community as well as lawmakers at home to give those penalties more time before considering military action.

"Iran is feeling the bite of these sanctions in a substantial way," the president said Tuesday.

Obama addressed Iran and other pressing international concerns amid a whirlwind of activity on that front. The United States and its allies are preparing to return to the negotiating table with Iran. The past few days have been consumed by talk of Iran, and the possibility of an Israel-led military strike, as Israeli Prime Minister Benjamin Netanyahu visits Washington. The Republican presidential candidates, who are battling on Tuesday across 10 state primaries and caucuses, have also criticized Obama as too dovish on Iran.

Obama on Tuesday decried what he described as the "casualness" with which some people talk of war, warning that this leads to "mistakes." He stressed there is a "window of opportunity where this can still be resolved diplomatically."

The president said he doesn't "expect a breakthrough" in the first meeting with Iran, but claimed the U.S. and its allies should have a sense "fairly quickly" about how serious Iran is about resolving the issue -- and about offering assurances that it is not pursuing a nuclear weapon.

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"We will not countenance Iran getting a nuclear weapon," Obama said, repeating his message from his weekend speech to the American Israel Public Affairs Committee. "My policy is not containment. My policy is to prevent them from getting a nuclear weapon," he said.

He said that step could trigger an arms race in the region, and risk such a weapon falling into the hands of terrorists.

Obama also took aim at his aspiring Republican presidential rivals -- suggesting they were the ones speaking most loosely about war with Iran and challenging them to justify their positions.

"Those folks don't have a lot of responsibilities. They're not commander in chief. And when I see the casualness with which some of these folks talk about war, I'm reminded of the costs involved in war," Obama said. "This is not a game. There is nothing casual about it."

Obama said if the candidates think it's time to launch a war, "they should say so."

Those candidates were sharply critical of Obama ahead of his press conference.

Rick Santorum criticized the joint offer by the United States, European countries, Russia and China to resume talks with Iran on its suspected nuclear weapons program as "another appeasement, another delay, another opportunity for them to go forward (with developing a nuclear weapon) while we talk."

Mitt Romney assailed the administration's go-slow approach on Iran, saying "the only thing respected by thugs and tyrants is our resolve, backed by our power and our readiness to use it."

And Newt Gingrich waded into the divide between Obama and Netanyahu of "red lines," or benchmarks in Iran's nuclear development, that might demand a military response. Israel believes it has a shorter time frame to act because it lacks the military technology of the United States to attack Iran's underground nuclear facilities.

"The red line is now," Gingrich declared to a standing ovation.

Iran's nuclear ambitions were commanding attention in the aftermath of Obama's meeting Monday with Netanyahu. Tension over Iran has already contributed to higher oil prices, and Israel's threats of pre-emptive military strikes to prevent Tehran from building a nuclear bomb have dominated Washington discourse for weeks.

The president also said Tuesday he disagreed with calls by several U.S. senators for the United States to launch airstrikes in Syria to protect the people of that country from Bashar Assad's regime.

"For us to take military action unilaterally, as someone suggested, or to think that somehow there is some simple solution, I think is a mistake," Obama said.

Sen. John McCain, R-Ariz., a day earlier called for airstrikes in Syria. He was later joined by Sens. Joe Lieberman, I-Conn., and Lindsey Graham, R-S.C.

Obama also pitched new mortgage relief for members of the military as well as homeowners with government-insured loans.

Obama announced plans to let borrowers with mortgages insured by the Federal Housing Administration refinance at lower rates, saving the average homeowner more than $1,000 a year. And Obama detailed an agreement with major lenders to compensate service members and veterans who were wrongfully foreclosed upon or denied lower interest rates.

Obama held the news conference in the midst of a modestly improving economy. But international challenges as well as a stubbornly depressed housing market remain threats to the current recovery and to his presidency.

Obama had not held a full news conference since November. The White House scheduled this one on the same day as the 10-state Super Tuesday Republican presidential nominating contests. While aides insisted the timing was coincidental, it follows a pattern of Obama seeking the limelight when the attention is on the GOP.

Asked Tuesday whether he had any words for Romney, Obama said: "Good luck tonight ... really."

The news conference comes amid a new sense of optimism at the White House. Obama's public approval ratings have inched up close to 50 percent. The president recently won an extension of a payroll tax cut that was a main element of his jobs plan for 2012. Economic signals suggest a recovery that is taking hold.

Still, the unemployment rate in January was 8.3 percent, the highest it has been in an election year since the Great Depression. With rising gasoline prices threatening to slow the economy, Obama has also faced attacks from Republicans over his energy policy.

Obama, though, ridiculed the notion Tuesday that he actually wants gas prices to rise in order to wean Americans off fossil fuels.

"Do you think the president of the United States going into reelection wants gas prices to go up higher?" he asked, rhetorically. "Here's the bottom line ... I want gas prices lower because they hurt families."

Under the housing plans Obama announced Tuesday, FHA-insured borrowers would be able to refinance their loans at half the fee that the FHA currently charges. FHA borrowers who want to refinance now must pay a fee of 1.15 percent of their balance every year. Officials say those fees make refinancing unappealing to many borrowers. The new plan will reduce that charge to 0.55 percent.

With mortgage rates at about 4 percent, the administration estimates a typical FHA borrower with $175,000 still owed on a home could reduce monthly payments to $915 a month and save $100 a month more than the borrower would have under current FHA fees.

Though 2 million to 3 million borrowers would be eligible, the administration official would not speculate how many would actually seek to benefit from the program. The FHA provides mortgage insurance on loans made by FHA-approved lenders throughout the United States and its territories. The loans typically go to homeowners who do not have enough equity to qualify for standard mortgages. It is the largest insurer of mortgages in the world.

For service members and veterans, under the plan major lenders would review foreclosures to determine whether they were done properly. If wrongly foreclosed upon, service members and veterans would be paid their lost equity and also be entitled to an additional $116,785 in compensation. That was a figure reached through an agreement with major lenders by the federal government and 49 state attorneys general.

Under the agreement, the lenders also would compensate service members who lost value in their homes when they were forced to sell them due to a military reassignment.

The Associated Press contributed to this report.