TOKYO — Shintaro Ishihara, the firebrand governor of Tokyo whose vocal campaign to secure a set of disputed islands provoked a damaging dispute with China, declared Thursday that he was quitting local politics to start a national party, a move that could win him some say in shaping policy and escalate the territorial dispute.

Mr. Ishihara, a nationalist politician who has said that Japan should develop nuclear weapons and abandon its pacifist Constitution, is considered too far right of the populace to build a party big enough to form a government. But with polls suggesting no clear winner in elections that must be called by August, Mr. Ishihara could potentially become an influential player in a coalition government and push its leaders to take a more nationalistic stance.

Some analysts acknowledged Mr. Ishihara’s potential to become a kingmaker, but said the electoral politics remain very fluid.

“If elections are called before the end of the year, he could become the eye of the storm,” Hirotada Asakawa, an independent political analyst, told the daily Kanagawa Shimbun. But he said that if the election were delayed, Mr. Ishihara could be exposed to more criticism of his record, like his gaffes and Tokyo’s failed bid to land the 2016 Olympics.