Mr. Ryu said North Korea would not change its plans. The launching jeopardizes a recent United States agreement with North Korea in which the North agreed to suspend uranium enrichment, thereby slowing its nuclear program, in return for food aid. American officials have reported that they explicitly said during negotiations that North Korea could not launch satellites, which analysts see as a cover for testing missile technology. Such missiles could eventually be fitted to deliver nuclear weapons.

On Tuesday, Jay Carney, the White House press secretary, said “it’s impossible to imagine that we would be able to follow through” with the food aid if North Korea moved ahead with a “flagrant violation” of its international obligations.

Secretary of State Hillary Rodham Clinton and Susan E. Rice, the United States ambassador to the United Nations, continued to try to exert pressure on Tuesday. Mrs. Clinton said the United States and its allies were still trying to persuade North Korea to stop the launching.

“We believe strength and security will not come from more provocations but from North Korea living up to its commitments and obligations,” Mrs. Clinton said, without elaborating on what retaliatory steps the United States would consider beyond withholding the food aid promised in February. She and Japan’s foreign minister, Koichiro Gemba, with whom she met Tuesday, said North Korea’s plans would be the forcus of meetings of the foreign ministers of the Group of 8 nations in Washington this week. Ms. Rice said the Security Council should convene and “respond credibly,” if the North goes ahead with its plans.

Canceling the launching, however, could put North Korea’s leader, Kim Jong-un, in a difficult position at home, where he is trying to shore up his power just months after his father’s death. The lofting of the satellite is timed to celebrations for the centenary of the birth of his grandfather, Kim Il-sung, the revered founding president, who was born April 15, 1912.