TOKYO, Sept 17 (Reuters) - Candidates to become Japan"s prime minister officially launch their campaigns on Friday, with popular vaccine minister Taro Kono expected to be the top contender to replace Yoshihide Suga. The leadership race for the ruling Liberal Democratic Party (LDP) took an unexpected turn two weeks ago when Suga said he would step down, setting off a heated fight. The winner of the Sept. 29 election will become prime minister by virtue of the party"s majority in the lower house of parliament. The LDP"s image has been battered by public perceptions that Suga bungled his handling of COVID-19. After his one year in office, party members are keen for a fresh face the carry them to victory in general elections expected within two months. The popular Kono, whose resume is studded with jobs including the foreign and defence portfolios, faces off against former foreign minister Fumio Kishida, Sanae Takaichi, who held the internal affairs ministry post, and Seiko Noda, a former minister for gender equality. Unlike in last year"s race, grassroots LDP members will join lawmakers in casting ballots. The media-savvy, U.S.-educated Kono, at 58 on the younger side for a Japanese premier, is widely seen as the frontrunner due to his popularity with the public, who regularly choose him as their favourite for prime minister. Investors have also recently warmed to Kono at Kishida"s expense. His chances were bolstered this week when LDP heavyweight Shigeru Ishiba, who is popular with the party rank and file and had been considering his own candidacy, threw his support behind Kono. But Kono has a reputation as a maverick, and elders in the faction-ridden LDP may favour the soft-spoken Kishida, 64, who hails from one of the party"s move dovish factions, due to perceptions he may be better than Kono at building consensus. Takaichi, 60, who is aiming to become Japan"s first female premier, is a disciple of former prime minister Shinzo Abe, Japan"s longest-serving premier, and a member of the LDP"s most conservative wing. Noda, 60, who joined the race on Thursday after winning the support of the required 20 lawmakers to throw her hat in the ring, is seen as a long shot. But she but could have an outsized impact on the race by making it harder for one candidate to win a majority in the first round. On economic policy, where Japan is struggling to recover from successive waves of the coronavirus, Kono wants any further stimulus to prioritise renewable energy and expansion of 5G networks, while Kishida says Japan should strive for a new form of capitalism to reduce income disparity.