WASHINGTON — President Bush said yesterday the Iraq war is “straining the psyche of our country” but that leaving now would be a disaster.

Mr. Bush served notice at a news conference that he would not change course or flinch from debate about the unpopular war as he campaigns for Republicans in the fall congressional elections. In fact, he suggested that national security and the economy should be the top political issues and criticized the Democrats’ approach on both.

Many Democrats want to leave Iraq “before the job is done,” the president said. “I can’t tell you exactly when it’s going to be done,” he said, but “if we ever give up the desire to help people who live in freedom, we will have lost our soul as a nation, as far as I’m concerned.”

Now in its fourth year, the war has taken a heavy toll — more than 2,600 Americans have died and, by some estimates, more than 100,000 Iraqis have been killed. Last month alone, about 3,500 Iraqis died violently, the highest monthly civilian toll so far. Mr. Bush’s approval rating has slumped to the lowest point of his presidency, and Republicans are concerned that they could lose control of Congress because of voters’ unhappiness.

Mr. Bush said he was frustrated by the war at times.

“War is not a time of joy,” he said. “These are challenging times, and they’re difficult times, and they’re straining the psyche of our country. I understand that. You know, nobody likes to see innocent people die. Nobody wants to turn on their TV on a daily basis and see havoc wrought by terrorists.”

But Mr. Bush said he agreed with the top American commander in the Middle East, General John Abizaid, that if “we leave before the mission is done, the terrorists will follow us here.” A failed Iraq would give extremists the revenue from oil sales, Mr. Bush said.

In response, Democrats said it was time for a new direction and that Mr. Bush should begin redeploying troops this year.

“Our soldiers in Iraq should transition to a more limited mission focused on counterterrorism, force protection of U.S. personnel and training, and logistical support of Iraqi security forces,” House Democratic Leader Nancy Pelosi said.

Senate Democratic Leader Harry Reid said, “Far from spreading freedom and democracy in the Middle East, the Bush administration has watched while extremists grow stronger, Iran goes nuclear, Iraq falls into civil war, and oil and gas prices skyrocket. Simply staying the course is unacceptable.”

Mr. Bush said differences over Iraq provide “an interesting debate.” “There’s a lot of people — good, decent people — saying ‘withdraw now.’ They’re absolutely wrong. … We’re not leaving, so long as I’m the president. That would be a huge mistake.”

“Leaving before the job is done would be a disaster.”

Mr. Bush said he would not question the patriotism of someone who disagreed with him — although Vice President Cheney said recently that the Democratic primary election victory of an anti-war candidate, Ned Lamont, over Senator Lieberman, a defender of the war, might encourage “the Al Qaeda types.”

Mr. Bush opened his nearly hour-long news conference by calling for quick deployment of an international force to help uphold the fragile cease-fire in southern Lebanon. “The need is urgent,” Mr. Bush said. He said America was increasing humanitarian and reconstruction aid to more than $230 million.

European countries expected to provide the bulk of peacekeepers have delayed committing troops. France disappointed allies by merely doubling its contingent of 200.

The president also said America would seek a new U.N. resolution on disarming Hezbollah in southern Lebanon, but he sounded doubtful about achieving results soon on the ground. “Hopefully, over time, Hezbollah will disarm,” the president said.

Mr. Bush also urged patience about the rebuilding of New Orleans and other gulf communities ravaged by Hurricane Katrina a year ago. The federal government has committed $110 billion to help. “I also want the people down there to understand that it’s going to take a while to recover,” the president said. “This was a huge storm.” He suggested the federal government had done its part and that state and local officials should move faster.

On other points, Mr. Bush said:

• He talked yesterday with President Hu of China about trying to revive six-party negotiations aimed getting North Korea to give up its nuclear ambitions. The White House said the two leaders, in a 21-minute call, also discussed economic issues that have caused friction.

• There is no quick fix for soaring gasoline prices. He said the answer was to diversify away from crude oil.

• A morning-after contraceptive pill, known as Plan B, should require a prescription for minors. Anti-abortion groups want Mr. Bush to withdraw Dr. Andrew von Eschenbach, his nominee to head the Food and Drug Administration because they think he will approve over-the-counter sales of the morning-after pill. Some Democrats, meanwhile, are upset that the FDA has long delayed settling the debate over whether at least some women could buy the contraceptive without a doctor’s note.