By Josh Smith

SEONGNAM, South Korea (Reuters) - South Korea will kick off its largest-ever defence exhibition this week, as the country seeks to turbocharge its arms sales and showcase a rare appearance by a U.S. nuclear-capable bomber.

The biennial Seoul International Aerospace and Defense Exhibition (ADEX) opens its doors on Tuesday, with organisers saying there will be more companies than ever and an unprecedented flyby from a U.S. B-52 bomber, which will make a rare landing at an airbase elsewhere on the peninsula.

This year’s show is designed to help South Korea to reach its goal of becoming the world’s fourth-largest arms exporter, Lee Jong-ho, chief of the organising office, told a briefing on Monday.

More than 450 senior defence officials from 54 countries are expected to attend, along with hundreds of thousands of other professionals and members of the public, he said.

"This is an opportunity for Korea's defence industry to draw international attention and take a giant leap forward," Lee said.

The Korean government has set a goal of reaching $20 billion in defence exports this year after sealing a record $17.3 billion in arms sales last year, including huge deals with Poland for tanks, howitzers, warplanes, and rockets.

South Korea has been roughly ninth in the world for defence exports in recent years, but President Yoon Suk Yeol has called for it to improve.

At a South Korean military airbase south of Seoul on Monday, exhibitors made final preparations as participants in early events wandered among South Korean and U.S. military vehicles and warplanes on the tarmac, including advanced American stealth F-22 and F-35 aircraft.

To commemorate the 70th anniversary of South Korea’s alliance with the United States, the show will feature a larger than usual display of American military power, including the B-52 flight said U.S. Air Force Colonel Charles Cameron.

Under Yoon, South Korea and the United States have stepped up displays of strength, particularly U.S. nuclear-capable assets, in an effort to deter North Korea.

Last month South Korea staged a rare military parade, in which thousands of troops and South Korea's home-grown tanks and self-propelled artillery were joined by 300 of the 28,500 U.S. soldiers based in the country.

A South Korean activist group said it planned to protest the event, calling the arms trade a "parasite" that benefits from the suffering in places such as Ukraine and the Israeli-Palestinian conflict.

(Reporting by Josh Smith)