SEOUL, South Korea - New South Korean President Lee Myung-bak took office Monday with a promise to boost prosperity not only in his own country but in North Korea as well -- provided the communist state abandons its nuclear weapons.

"Economic revival is our most urgent task," Lee said in his inaugural speech after taking the oath of office as South Korea's first conservative president in a decade.

South Koreans gave the former high-profile construction executive a landslide victory in December's election on his pledge to revitalize the economy and take a less conciliatory approach to nuclear-armed North Korea.

"We must move from the age of ideology into the age of pragmatism," Lee told some 60,000 people who gathered for his inauguration, taking a swipe at the past 10 years of liberal rule during which he said "we found ourselves faltering and confused."

Lee, a former construction CEO nicknamed "The Bulldozer" for his can-do image, took the oath of office at the National Assembly in the presence of cheering onlookers, foreign dignitaries including Secretary of State Condoleezza Rice and a choir singing Beethoven's "Ode to Joy."

Lee, 66, also called for a stronger alliance with top ally Washington and implored North Korea to forgo its nuclear ambitions and open up to the outside world, promising a better future for the impoverished nation.

Rice, speaking to reporters separately, hailed Washington's ties with Seoul.

"It is a relationship that has only deepened over the years because we share something very important," she said. "As much as we share strategic interests we certainly share common values."

Lee said he would launch massive investment and aid projects in the North to increase its per capita income to $3,000 within a decade "once North Korea abandons its nuclear program and chooses the path to openness."

Lee is the 10th man to serve as South Korea's president and the first to come from a business background.

He wooed voters by promising to reach annual economic growth of 7 per cent, double the country's per capita income to $40,000 over a decade and make South Korea one of the world's top seven economies.

South Korea's economy grew 4.9 per cent last year and 5 per cent the year before, but Lee says it has underperformed.

The country's benchmark stock market rose 1.3 per cent Monday on investor expectations of stronger economic growth under Lee.

"I have high expectations that Lee Myung-bak will revive our economy," Cho Han-keum, who runs a shelter for elderly homeless people, said at the inauguration site.

One analyst was more cautionary.

"One of the sternest challenges Mr. Lee will face is the weight of expectations he has manufactured," said Daniel Melser, senior economist at Moody's Economy.com. "Global economic conditions have soured ever since Lee made this promise late last year."

In his first meeting with a foreign leader as president, Lee and Japanese Prime Minister Yasuo Fukuda agreed to hold a summits on a regular basis and consider reviving stalled free trade talks, Lee's spokesman Lee Dong-kwan said.

"It was a bright, forward-looking discussion," Fukuda told reporters after the meeting. He said the two countries have many areas in which they can cooperate, including regional security.

Lee's predecessor Roh Moo-hyun and former Japanese Prime Minister Junichiro Koizumi initiated "shuttle diplomacy" in 2004, but it was suspended the following year amid disputes over history and the countries' competing claims to a set of islets in waters dividing them.

Lee agreed to visit Japan in April, with Fukuda to make a return visit in the second half of the year, the spokesman said.

Though Lee has vowed to broadly continue Seoul's policy of detente with the North, he has said he will approach the country with a more critical eye.

His predecessors -- Roh Moo-hyun and Kim Dae-jung -- were accused of showering unconditional aid and concessions as part of reconciliation efforts while getting little in return.

Lee said he is willing to meet North Korean leader Kim Jong Il whenever necessary.

"Indeed, the opportunity is open," Lee said.

Both Kim and Roh traveled to Pyongyang for summits.

North Korea has made no comment on Lee since his election.

International talks on North Korea reported significant progress last year after Pyongyang shut down its main nuclear reactor and began disabling key atomic facilities.

The talks, however, have not been held since October because of a dispute over whether Pyongyang kept its promise to declare all its nuclear programs by the end of December.

The Japan-born Lee first gained prominence as head of the massive Hyundai conglomerate's construction unit, which helped build South Korea during its miraculous economic rise in the 1960-70s. He became chief executive officer at age 35 and later served as a national legislator and mayor of Seoul.