FACTBOX-Likely scenarios after Japan PM Fukuda resigned

(Reuters) - Whoever succeeds Prime Minister Yasuo Fukuda following his abrupt resignation on Monday faces big problems, including a deadlocked parliament and pressure to call an early election.

Opposition parties took control of parliament's upper house last year, enabling them to delay parliamentary decisions for months.

An election for the more powerful lower chamber, where the Liberal Democratic Party-led ruling bloc holds a huge majority, must be held by September 2009.

The following are some possible political scenarios.

* Frontrunner LDP Secretary-General Taro Aso, or another candidate, wins a party leadership election expected this month, rebuilds the government's popularity and calls a general election towards the end of this year or early in 2009.

But even a strong performance in the election could leave the LDP and its junior coalition partner worse off in the lower house, and would do nothing to resolve the stand-off with the upper house. The LDP would have to try to lure opposition politicians to boost its ranks in the upper chamber.

* The new prime minister fails to boost the LDP's popularity, and delays the general election until after the budget is passed in March of next year or even closer to the end of lower house lawmakers' terms in September 2009.

The main opposition Democratic Party would then have a chance at forming a government, ejecting the LDP from power for only the second time in its 63-year history.

* There could be a realignment of loyalties among members of the ruling coalition and opposition parties, in an effort to forge a coherent majority in both houses. This could be formed along policy lines or based on personal ties. Currently, both the LDP and the Democrats are mixed bags of lawmakers from across the political spectrum, while in many ways the junior coalition partner, the New Komeito, is closer in policies to the Democrats.

(Reporting by Isabel Reynolds; Editing by Rodney Joyce)