TOKYO - Japanese Prime Minister Yukio Hatoyama said on Tuesday he is finalizing a plan to resolve a row over a US airbase by an end-of-May deadline, as he struggles to revive sagging support in the run-up to an election.

Hatoyama spoke to reporters hours ahead of the arrival of a key US envoy who said in a newspaper interview published on Tuesday that Japan had presented a "serious" proposal that could enable talks to progress to a new level.

"The situation is that we are considering a government proposal seriously," Hatoyama told reporters outside his residence. "I want to put the final touches to it." But he said working-level talks on the plan between Japan and the US had not yet begun.