By Linda Sieg and Yoko Kubota
TOKYO (Reuters) - Japanese Foreign Minister Seiji Maehara decided Sunday to resign for taking donations from a foreign national, domestic media said, adding to unpopular Prime Minister Naoto Kan's troubles as he battles to keep his own job.
Maehara, a security hawk who favors close ties with the United States and has criticized China's defense buildup, has been seen as a key contender to replace the embattled Kan if he bows to pressure to step down himself.
Kyodo news agency said Maehara had rejected a plea from Kan to stay in his post.
Maehara's resignation would deepen the impression of a government in disarray, adding to pressure on Kan as he fights to keep his own party from unraveling and avoid calling a snap election while trying to enact budget bills in a hung parliament.
The stalemate is blocking the passage of bills needed to implement a $1 trillion budget for the fiscal year from April.
It is also keeping Kan from getting opposition help on tax reforms, including a rise in the 5 percent sales tax, that he argues are vital to fund the costs of a fast-aging society and curb public debt now twice the size of the $5 trillion economy.
Kan, whose voter ratings have slid to around 20 percent, himself faces calls from within his own fractious Democratic Party to resign, while opposition parties are pushing him to call a snap election that the Democrats could well lose.
Opposition parties were quick to turn up the heat on Kan.
"We will take issue with the Prime Minister's responsibility in having appointed him (Maehara)," Kyodo news agency quoted main opposition Liberal Democratic Party (LDP) policy chief Shigeru Ishiba as saying after reports that Maehara wanted to quit.
PUSH FOR POLL
Kyodo added that the LDP would step up its push for an election for parliament's powerful lower house, a poll that the ruling Democratic Party is in danger of losing if held soon.
The second-biggest opposition party, the New Komeito, echoed the criticism.
"This is symbolic of Kan's government, which has lost the public's confidence. The prime minister's responsibility will be greatly questioned, Kyodo quoted New Komeito executive Yoshio Urushibara as saying.
An election, however, would not resolve the problem of a divided parliament since no single party would hold a majority in both houses, no matter who wins.
"It's impossible for him to call a snap election. Momentum will build for Kan to resign," said Nihon University political science professor Tomoaki Iwai.
But he added that Kan was unlikely to quit without assurances from opposition parties that they would help enact the stalled budget bills, something they might well be unwilling to provide, especially ahead of nationwide local elections in April.
Maehara had admitted Friday accepting donations from a Korean resident of Japan, but said he had done so unknowingly. Taking political donations from foreign nationals is illegal if done intentionally.
Earlier Sunday Japan's second-biggest opposition party had called on Maehara to resign.
"A foreign minister is at the forefront of negotiations with foreign countries. If a person in that post has taken donations from foreign nationals, resignation is unavoidable," Yosuke Takagi, acting secretary-general of the New Komeito, said in a televised debate.
Hirofumi Nakasone, head of the LDP's upper house caucus, echoed the call, saying at another TV debate program that Maehara should "take responsibility" for the donations.
(Additional reporting by Kiyoshi Takenaka, Chisa Fujioka and Shinsuke Saoshiro; Editing by Joseph Radford)