TOKYO , June 4, 2010: Naoto Kan, Japan’s Finance Minister, moved into pole position in the race to succeed outgoing Prime Minister Yukio Hatoyama and claim the top post as Japan’s fifth prime minister in four years, as influential cabinet members pledged to support him, ruling party lawmakers said Thursday.

Leading lawmakers in the governing Democratic Party threw their support behind Mr. Kan, a sharp-tongued political veteran who earned a name for himself by battling Japan’s powerful bureaucrats. His reputation made it increasingly unlikely that he would face serious opposition on Friday, when the party holds an internal vote to choose a successor for Mr. Hatoyama.

Okada and Maehara were both tipped to be strong contenders with Okada asked for his backing by Kan in talks Thursday morning. Okada agreed providing Kan, in his new role as DPJ boss, does not run the party from the shadow of backroom dealer Secretary- General Ichiro Ozawa, who will step down with Hatoyama Friday, but is likely to still be able to exert political influence in a new role from behind the scenes.

Apparently caught off guard by Mr. Hatoyama’s sudden decision to resign over broken campaign promises, the Democrats have moved quickly to find a replacement and to try to win back public trust. They face an uphill battle in regaining the momentum they had in August after winning a landslide election victory that ended a half-century of virtual one-party rule in Japan.

The party is apparently betting that Mr. Kan’s background as a former civic activist who rose through the opposition will make him a more forceful leader than the indecisive and professorial Mr. Hatoyama, who squandered last summer’s historic election mandate.

Known for his quick temper, Mr. Kan, 63, gained national attention in the mid-1990s when as health minister he exposed the use of H.I.V.-tainted blood. In the Hatoyama administration, he also served as deputy prime minister and was a point man in the party’s push to rein in secretive central ministries that have run Japan since World War II. On Thursday morning, Japanese newspapers were predicting that Mr. Kan would be the next prime minister — even before he announced his candidacy later in the day. Other possible contenders, like Foreign Minister Katsuya Okada and Seiji Maehara, the transport minister, have declared their support for Mr. Kan. Whoever is chosen in Friday’s party ballot will later in the day face a vote in the lower house of Parliament for prime minister. The Democrats’ commanding majority in that chamber means that their candidate is virtually assured of winning. The newly selected prime minister must then go through the formality of being appointed by Emperor Akihito.