GIMPO, South Korea - As troops stood guard and a choir sang carols yesterday, South Koreans lit a massive steel Christmas tree that overlooks the world's most heavily armed border and is within sight of atheist North Korea.

The lighting of the tree after a seven-year hiatus marked a pointed return to a tradition condemned in Pyongyang as propaganda. The provocative ceremony - which needed government permission - was also a sign that President Lee Myung-bak's administration is serious about countering the North's aggression with measures of its own in the wake of an artillery attack that killed four South Koreans last month.

While the North has made some conciliatory gestures in recent days - indicating to a visiting U.S. governor that it might allow international inspections of its nuclear programs - Seoul appears unmoved.

Pyongyang has used a combination of aggression and reconciliation before to extract concessions from the international community, and the resurrection of the tree lighting at Aegibong is a signal that the South is ready to play hardball until it sees real change from the North.

Earlier, a South Korean destroyer prowled the sea and fighter jets tore across the skies in preparation for possible North Korean attacks a day after Seoul held a round of artillery drills from a front-line island.

After warning of deadly retaliation, North Korea said it would not deign to fight back, and indicated to visiting New Mexico Gov. Bill Richardson that it was prepared to consider ways to work with the South on restoring security along the tense border.

The White House, however, rejected the idea, saying Pyongyang needed to change its "belligerent" behavior first and was not "even remotely ready" for negotiations.

Press secretary Robert Gibbs said yesterday there were no plans to debrief Richardson after his trip. What Washington wants from the North, he said, is conciliatory deeds, not words.

In Seoul, a senior South Korean government official said the military would remain prepared for the possibility of a "surprise" attack in coming days. He spoke on condition of anonymity.

On Aegibong Peak, about a mile from the demilitarized zone (DMZ) that divides the Korean peninsula, armed marines circled the Christmas tree as more than 100,000 twinkling lights blinked on. The brightly lit tree - with a cross on top - stood in stark relief to North Korea, where electricity is limited.

Choir members dressed in white robes trimmed in blue and wearing red scarves and Santa Claus hats gathered beneath the steel structure draped with multicolored lights, illuminated stars and snowflakes. An audience of about 200 listened as they sang "Joy to the World" and other Christmas carols.

"I hope that Christ's love and peace will spread to the North Korean people," said Lee Young-hoon, a pastor of the Seoul church that organized the lighting ceremony. About 30 percent of South Koreans are Christian.

The 100-foot-tall steel tree sits on a peak high enough for North Koreans living in border towns to see it and well within reach of their nation's artillery. Defense Minister Kim Kwan-jin said an attack from North Korea was certainly possible but unlikely.

North Korea, officially atheist and with only a handful of sanctioned churches in Pyongyang with services for foreigners, warned that lighting the tree would constitute a "dangerous, rash act" with the potential to trigger a war.

"The danger of the enemy's threat still exists," the leaflet read, suggesting that they hide behind concrete walls, crouch down between chairs and move quickly to shelters in case of an attack.

The event took place uninterrupted.

For decades, the rival Koreas have fought an ideological war, using leaflets, loudspeakers and radio broadcasts across the border. At the height of the propaganda, South Korea's military speakers blared messages near the border 20 hours a day, officials say.

South Korea halted the campaign about seven years ago - including the longtime practice of lighting the huge Christmas tree - as ties between North and South warmed under an era of reconciliation.

Kim, the defense minister, said Seoul is also prepared to resume the use of loudspeakers installed near the DMZ, a move Pyongyang has warned would draw fire.