TOKYO -- Japan's two biggest parties Monday failed to break a deadlock in the search for a new prime minister to replace Tsutomu Hata who stepped down on Saturday.With the U.S. dollar falling to a record low below 100 yen in Tokyo, the turmoil brought on by Hata's resignation added to worries among economists and businessmen. None of the three blocs jockeying for power -- Hata's coalition, the Liberal Democratic Party and the Socialists -- hold a majority in parliament. Hata, who headed a minority government resigned to forestall a no-confidence motion but stays on as caretaker until parliament chooses a successor. If none of the blocs can form a government soon enough, Hata could be forced to represent Japan at the Naples Summit of the Group of Seven industrialized democracies, scheduled for July 8 to 10. It would be the second consecutive year that a Japanese lame-duck leader had sat at the summit table. In Monday's first round of talks, the Liberal Democrats and the Socialists were only able to agree they must make efforts to fill the political vacuum quickly. "The aim is to break the deadlock by selecting a successor prime minister as soon as possible," said a terse statement from the two parties after talks between Liberal Democrat head Yohei Kono and Socialist chief Tomiichi. They said they would work to choose a new prime minister by Tuesday, but lawmakers dismissed that as lip-service intended for the public, disgusted with endless political squabbles.