In a , Mr. Bush said the United States remains committed to diplomacy but also "reserves all options to defend our friends in the region."
He also vowed increased military cooperation with allies, including bolstering ballistic missile defenses in the region and increased efforts to prevent Pyongyang from importing missile and nuclear technology.
"With both Iran and North Korea on the agenda on Wednesday, the ability of the Security Council to pressure both nations to get back to negotiations and halt their nuclear programs is being seen as a test of the U.N. to keep a nuclear weapons race from spiraling out of control," says CBS News foreign affairs analyst Pamela Falk.
"South Korea's Foreign Minister, Ban Ki Moon, as the soon-to-be-appointed next Secretary-General, will be at U.N. headquarters as well," Falk says, "making his first appearance since the Security Council chose him to succeed Kofi Annan."
Mr. Bush rejected international appeals — such as one made as he spoke by Annan — for the United States to hold one-on-one talks with North Korea, something the U.S. has refused to do.
In a news conference that lasted slightly more than an hour, Mr. Bush also defended anew his Iraq policy against rising calls, mostly from Democrats but also from some in his own party, to set a withdrawal timetable. "If we were to leave before the job is done, the enemy's coming after us," he asserted.
Mr. Bush conceded "tough times" in the war-torn country where sectarian violence has surged recently. But, he added, "It is in our interests that Iraq succeed."
With just four weeks before the midterm elections, the president acknowledged that the war in Iraq is having a political impact. It is "tough on the American psyche," he said, repeating a phrase he had used before.
Mr. Bush said there were "loud voices" in the Democratic Party for him to withdraw troops, bur added that he was not going to "get out before the job is done."
"I think the elections will be decided by security and the economy," he said, pointing to signs of significant improvement in job creation, lower energy prices and tax cuts that he said are working. He opened his news conference by trumpeting new figures showing a big reduction in the U.S. budget deficit.
Mr. Bush predicted that his party would maintain control of both the House and Senate in next month's midterm elections. In the House, Democrats need a 15-seat pickup to gain control. In the Senate, they need to gain six seats.
The president issued strong support for embattled House Speaker Dennis Hastert's handling of a scandal involving salacious Internet communications between former Rep. Mark Foley, R-Fla., and teenage male former congressional pages.
"I think the speaker's strong statements have made it clear to not only the party ... but to the country, that he wants to find out the facts," Mr. Bush said. "This is disgusting behavior when a member of Congress betrays the trust of the Congress and the family that sent a young page to serve."
He said he hopes that congressional and Justice Department investigations "find the facts" and that he hoped it was "sooner, rather than later," but said he doesn't think the scandal has undermined Hastert's credibility as a leader.
"Denny's very credible, as far as I'm concerned," he said.
Most of the questions at the news conference dealt with North Korea, with Iraq a close second.
Mr. Bush rejected criticism from Democrats that his administration had not paid enough attention to the brewing North Korean nuclear crisis. "The North Korean situation was serious for years," he said in a veiled swipe at former President Clinton.
The president said Pyongyang had broken a 1994 deal negotiated by the Clinton administration in which Pyongyang had promised not to develop a nuclear program.
"It's the intransigence of the North Korean leader that speaks volumes about the process," he said of Kim Jong Il. "It is his unwillingness to choose a way forward for this country — a better way forward for his country. It is his decisions."
As to direct talks with North Korea, as the U.N. secretary-general and many other diplomats have urged, Bush suggested that the Clinton administration's direct contacts with the communist regime showed they were unprofitable.
"Bilateral negotiations didn't work. You know, I appreciate the efforts of previous administrations. It just didn't work," Mr. Bush said. He called for a resumption of six-way talks among North Korea, South Korea, China, Russia, Japan and the United States. Such talks have been suspended since November 2005.
Mr. Bush said that North Korea with its actions "has once again chosen to reject the prospect for a better future."
North Korea has said one reason it tested an atomic weapon is to stave off an Iraq-style pre-emptive attack by the United States. But Mr. Bush said: "The United States affirmed that we have no nuclear weapons on the Korean Peninsula. We affirmed that we have no intention of attacking North Korea."
In answer to a question he asked himself — why the United States doesn't take military action against North Korea — the president said: "I believe the commander in chief must try all diplomatic measures before we commit our military."
He was asked about a recent comment by the Republican chairman of the Senate Armed Services Committee, Sen. John Warner, that Iraq was drifting "sideways" and that the United States should consider major changes if Baghdad doesn't get the violence under control within the next few months.
"I appreciate Sen. Warner going over there and taking a look," the president said. "I completely agree."
Still, he insisted, "We're constantly changing tactics."
Warner is one of several prominent Republicans who have expressed misgivings recently about the course of U.S. policy in Iraq.
Mr. Bush dismissed as "just not credible" a controversial new study that contends nearly 655,000 Iraqis have died because of the war. The study was based on interviews by researchers with Iraqi families and suggests a far higher death toll than other estimates.
However, the president, who in the past has suggested 30,000 civilian deaths in Iraq, would not give a figure for overall fatalities. "I do know that a lot of innocent people have died," he said.
On another subject, Bush was asked about legislation authorizing construction of a 700-mile fence along parts of the U.S.-Mexican border and whether the fence would be solid and unbroken, or a "virtual fence" that relies on electronic sensors.
"We're going to do both," he said "Make sure we're going to build it in a spot where it works. " He added that the fence, on which construction has already begun, would be a combination of an actual barrier and electronics.
"You can't fence the entire border," he said
Mr. Bush also used the opportunity to put in a plug for his proposal, stymied so far in Congress, to establish a guest-worker program "so people aren't sneaking in in the first place."