* Seoul says N.Korean involvement in Games lowering tensions
* N.Korea expresses outrage at Kim photo burning protest
* Pyongyang announces new military anniversary on eve of Olympics
* Pence says will seek to counter effort to 'hijack' games (Adds U.S. vice president, background, paragraphs 10-11, 21)
By Hyonhee Shin
SEOUL, Jan 23 (Reuters) - The South Korean government rejected criticism on Tuesday that next month's Winter Olympics had been hijacked by North Korea, saying the Games will help defuse tensions over Pyongyang's nuclear and missile programmes.
Some opposition politicians and conservatives in South Korea have criticised North Korea's participation in the Games to be held in the South Korean alpine resort of Pyeongchang, dubbing them the "Pyongyang Olympics".
"Just one month ago, acute tensions gripped the Korean peninsula, South Korean presidential spokesman Park Soo-hyun told a news conference, referring to a crisis over North Korea's efforts to develop nuclear-tipped missiles capable of hitting the United States.
"We're confident that the Olympics will be a stepping stone to bring peace to the Korean peninsula, to Northeast Asia and the world," he said.
The two Koreas held the their first formal talks in nearly two years this month and the South agreed to help arrange for the North to join the Games.
Some specific plans, including for a joint women's ice hockey team and marching under a united flag, have proven controversial, with conservatives and younger South Koreans upset that North Korean leader Kim Jong Un is stealing the spotlight.
The administration of South Korea's liberal president, Moon Jae-in, is also under pressure over its offer to send athletes to a North Korean ski resort for joint training. Experts say the move risks giving Kim's heavily sanctioned government legitimacy and some much-needed cash.
Seoul officials are on a three-day trip to the North starting on Tuesday to inspect the resort's facilities and the newly built Kalma Airport nearby that may be used to fly in the South Korean skiers, who are not expected to attend the Games.
Moon's approval rating has fallen to a four-month low at 66 percent, a poll showed on Monday, due to a backlash over the decision regarding the combined ice hockey team.
U.S. Vice President Mike Pence, who will represent the United States at the Olympics, said on Tuesday he would seek to counter what he called Kim’s effort to "hijack" the Games with a propaganda campaign, a White House official said.
President Donald Trump and top advisers have publicly welcomed the intra-Korean talks, but U.S. officials have warned that Pyongyang might be trying to drive a wedge between Washington and its South Korean ally.
North Korea will send a 15-strong ice hockey team to the South on Thursday to train with South Korean players, together with a group of officials who will inspect Olympics facilities, Seoul's Unification Ministry said.
It said the Koreas had also finalised venues for joint orchestra performances on Feb. 8 at Gangneung, near Pyeongchang, and on Feb. 11 in Seoul.
Small but vocal groups of demonstrators protested at Seoul's central train station on Monday, where a North Korean delegation had arrived to see the concert venues. Protesters burned a picture of Kim and one placard read: "We're opposed to Kim Jong Un's Pyongyang Olympics!".
North Korea's Committee for the Peaceful Reunification of the Country, in charge of inter-Korean affairs, called the picture-burning a "shuddering, hideous crime". It urged Seoul to apologise and punish those involved.
"We will never tolerate hideous acts of the conservative hooligans who insulted the sacred dignity and symbol of the DPRK, and the dishonest behaviour of the South Korean authorities who connived at such acts," North Korea's official news agency quoted a spokesman for the committee as saying.
The Democratic People's Republic of Korea is North Korea's formal name.
Separately, North Korea announced on Tuesday it would celebrate the founding of its military on Feb. 8 - the day before the start of the Games.
The anniversary was previously celebrated on April 25 and marked with a large military parade.
The South Korean military said a detailed analysis was needed to understand the reason for the date change.
Cheong Seong-chang, a senior fellow at South Korea's Sejong Institute think tank, said it could be part of an attempt to steal the show from South Korea, and that North Korea might use the parade to unveil weapons such as a new intercontinental ballistic missile. (Reporting by Hyonhee Shin; additional reporting by Matt Spetalnick, David Brunnstrom and Jeff Mason; Editing by Lincoln Feast, Janet Lawrence and Paul Tait)