TOKYO, Sept 18 (Reuters) - Two of the candidates vying to become Japan"s next prime minister denied on Saturday they had toned down their positions on nuclear energy and gender issues to attract conservative backing in a tight ruling party leadership election this month. The winner of the Sept. 29 contest to lead the Liberal Democratic Party (LDP) is almost certain to succeed Yoshihide Suga as the country"s next premier because the party has a majority in the lower house. Suga announced he would step down two weeks ago amid sinking approval ratings, triggering the leadership race between four candidates. read more They are vaccine minister Taro Kono, 58, former foreign minister Fumio Kishida, 64, Sanae Takaichi, 60, a former internal affairs minister from the party"s most conservative wing, and Seiko Noda, 61, a former minister for gender equality. Surveys of voters show Kono is their top choice, a key factor ahead of a general election due by November. But the social-media savvy, U.S.-educated Kono, who has also served as foreign and defence minister, is widely seen as a maverick - an image that worries many veteran party members. Contenders need to attract votes from grassroots party members and younger lawmakers, who are more likely to be swayed by popularity ratings, while also garnering support from party bosses who remain influential. A Kyodo news agency poll showed on Saturday that 48.6% of grassroots party members surveyed support Kono, followed by Kishida"s 18.5%, Takaichi"s 15.7% and 3.3% for Noda. Long seen as a critic of nuclear power, Kono rejected the suggestion that he had flip-flopped on the issue. "What I"ve been saying about an exit from nuclear power is decommissioning quickly nuclear power plants that are reaching retirement and gradually exiting nuclear energy," he said in a televised debate. "As I explained before, we should stop the use of coal, increase energy conservation and renewable energy and nuclear power can be used to fill the gap," he added. DIALOGUE WITH CHINA Kishida, a more traditional LDP consensus-builder saddled with a bland image, was asked whether he had back-pedalled over allowing married couples to have separate surnames. Japanese law does not permit that option, and a change is strongly opposed by conservatives - including candidate Takaichi - on the grounds that it would undermine family values. Asked about the impression that he had earlier favoured the change, Kishida said he recognised diversity but that questions remained as to how to treat children"s names under a new system. "At least considering the broad understanding of the people, I think that discussion is necessary now," he said. During a broad debate on topics ranging from COVID-19 to pensions and diplomacy, Kono called for dialogue with China amid growing concerns about its maritime assertiveness - a stance echoed by Kishida. "(Japan-China) summit meetings should be held regularly," Kono said. "Perhaps, we should tell the Chinese leadership to exert their power as one of players in the international order, not in the way of expansionism." Highlighting the predominant view emerging among politicians ahead of the general election, Kishida - considered the most hawkish on fiscal policy among the candidates - said he would not raise the sales tax rate for a decade and instead prioritise revitalising the economy over fiscal reform. The uncertain outcome of the LDP race contrasts with last year, when Suga quickly emerged as the leading candidate after Shinzo Abe quit citing ill-health after a nearly eight-year term that made him Japan"s longest serving premier. Party factions coalesced around Suga, Abe"s long-time lieutenant, and grassroots members had minimal say. This time, most factions are not unified and rank-and-file members will be apportioned the same number of votes as lawmakers. If no candidate takes a majority in a first round, a run-off between the top two will be held and grassroots members" votes will be diluted, potentially boosting Kishida"s chances against Kono. Takaichi and Noda, both vying to become the country"s first female prime minister, are seen as long-shots, although Takaichi has the backing of Abe and other party conservatives.