SEOUL, South Korea — At a time when dynastic rule is under attack in popular uprisings throughout the Middle East, the heir apparent to the North Korean dictator Kim Jong Il smoothly acceded to a senior position on the National Defense Commission, the country’s most powerful body, according to a report on Wednesday by a leading newspaper in Seoul.

The newspaper, the Chosun Ilbo, citing an unidentified source in North Korea, said Kim’s youngest son, Kim Jong Un, had cemented his position as the second most powerful person in the country when he was named recently to the post of vice chairman of the defense commission, which is led by his father.

The move was announced at a mass gathering of military leaders and security officials on Feb. 10, according to the newspaper’s source, but emerged only Wednesday, as the 69th birthday festivities for the elder Kim were in full swing in the nation’s capital, Pyongyang.

The celebration, typically crowned by a vast turnout of goose-stepping soldiers and dancing, uniformed women in the city’s central square, was punctuated — as it is every year — by a flower show featuring bright red tuberous begonias called kimjongilia.

Yet the events were marred by the leader’s failure to follow through on a promise of a day’s food to all of the country’s 24 million people, The Associated Press reported. The North, chronically short of food, is reportedly slipping into a deep crisis, and defectors cited by a South Korean website, Open Radio for North Korea, said the government could not afford to deplete its already meager stockpiles.

The government may also be saving up for 2012, the centennial of the birth of the country’s founder, Kim Il Sung, and the year the ailing Kim has heralded as a deadline for building a “powerful, prosperous” nation. Kim suffered a stroke in 2008 and is thought to have diabetes, kidney failure and cardiovascular problems.

The South Korean government marked his 69th birthday by sending “unification balloons” carrying 100,000 propaganda leaflets over the border, a South Korean website, the Daily NK, reported. At a ceremony before the launching, a lawmaker with the governing Grand National Party in South Korea, Lee Doo-ah, read a statement saying, “The succession from Kim Jong Il to Kim Jong Un is a violation of the universal and reasonable values of human beings and a tragic act against history.”

Just days before Kim’s birthday, his second son, Kim Jong Chol, 30, was in Singapore attending a concert by the legendary guitarist Eric Clapton, Agence France-Presse and other news outlets reported. Amateur video from the scene showed a young man bearing a strong family resemblance strolling through the venue trailed by men in civilian clothes who tried to shield him from the cameras. Apparently a dedicated fan, Kim Jong Chol attended a series of Clapton concerts in 2006, following the British star to performances in four German cities, AFP reported.

The North’s official Korean Central News Agency also said that with the day’s festivities the country was “paying high tribute to the undying feats that General Secretary Kim Jong Il has performed by leading the cause of building a thriving nation to victory.”

South Korean government officials could not immediately confirm Kim Jong Un’s promotion, and the North Korean news agency had made no mention of it by Wednesday afternoon.

“Kim Jong Un assuming such a position is quite natural, and not surprising,” said Paik Hak-soon, director of the Center for North Korean Studies at the Sejong Institute near Seoul. “It’s not too early for something like this. Sooner or later it was to be expected.”

Kim Jong Un, who is believed to be 28 or 29, appeared publicly for the first time at a meeting of the ruling Workers’ Party last fall. He was given the rank of four-star general and received two significant political posts: membership on the party’s Central Committee and a vice chairmanship of its Central Military Committee, which is also overseen by his father.

Although his emergence as a serious political figure has been undeniable, some political experts had remained unconvinced that Kim Jong Un was secure in his anointed position. But if the report of his promotion to the No. 2 post on the National Defense Commission is true, they said Wednesday, there can be no further doubts.

“He is in a very special and unique category, and nobody else can be included as possibly assuming the supreme leadership,” Paik said.

The 15-member defense commission has several vice chairmen, including Jang Song Taek, the leader’s brother-in-law and the younger Kim’s uncle. It is widely believed that Jang, the husband of Kim Jong Il’s sister, has effective day-to-day control of the country.

But in terms of power and position, “Kim Jong Un is already ahead of Jang Song Taek,” Paik said.

“Jang Song Taek is the most powerful and loyal guardian” for the heir apparent, he said. “But it’s not possible for him to be promoted to supreme leader.”

North Korea watchers in the South, lacking reliable and verifiable information about the North’s succession drama, were abuzz recently over television images showing the senior and junior Kims at an art show in Pyongyang: both men were wearing black pants, identical padded and oversize cargo coats and matching brown fur hats.