SEOUL, Feb 5 (Reuters) - North Korea may be preparing to test fire its longest range ballistic missile, possibly toward Japan, media reports have said. (For a full story, double-click on [ID:nSP393526)

Here are questions and answers as to why North Korea might test launch its Taepodong-2 missile:

WHAT DOES THE NORTH STAND TO GAIN BY LAUNCHING THIS MISSILE?

If the launch is successful, North Korea will have a missile with a maximum estimated range of 6,700 km (4,200 miles), designed to carry a nuclear warhead that can hit U.S. territory but not the continental 48 states. This would for the first time pose a direct security threat by the North to the United States.

The North, which already has hundreds of rudimentary missiles, would be able to test its multi-stage rocket systems and increase its ability to produce long-range missiles.

HOW BIG A THREAT IS THE TAEPODONG-2?

The only time North Korea has fired the missile was in 2006 when it managed just a few seconds of controlled flight and broke apart in less than a minute.

It has a crude multi-stage design and poor guidance system and takes weeks to prepare for launch. U.S. spy satellites can easily monitor the preparations and it should be relatively easy to destroy long before launch.

Experts have said North Korea does not yet have the technology to miniaturise a nuclear device to use as a warhead. But the North has been working on placing biological and chemical weapons on missiles.

WHAT DOES NORTH KOREA RISK BY TEST-FIRING THE MISSILE?

Another failed launch would be a major embarrassment for Pyongyang which has little beyond its military threat to win concessions from the outside world. That, and the high cost for the impoverished state, may make it reluctant to risk a second launch.

Its leaders may be happy to simply imply a threat by moving around missile-related equipment, knowing it will be seen by U.S. intelligence and raise alarm with the new U.S. government.

On the other hand, the international community has few options left to punish the North for a launch. North Korea is already subject to U.N. sanctions stemming from its 2006 ballistic missile test in July and nuclear test a few months after that. The United States has already called for a suspension of aid promised under a six-way nuclear deal while Japan and South Korea have blocked channels that sent cash and food to the impoverished state.

WHAT WILL NORTH KOREA SAY ABOUT THE LAUNCH?

North Korea will likely claim that a launch of the Taepodong-2 is for its civilian space and satellite programme and argue that under international law, it has the right to peacefully explore space. It will argue that its rival Japan already has a rocket programme and its neighbour South Korea is developing one.

A successful launch would be portrayed as a mighty symbol of leader Kim Jong-il's ideas and shore up his leadership after a suspected stroke in August raised questions about his grip on power.

The North would also tell its people that it has launched a rocket to carry a satellite ahead of its rich Southern neighbour while signalling to new U.S. President Barack Obama that Pyongyang should not be ignored.

WHEN MIGHT A LAUNCH TAKE PLACE

The North may time a launch to coincide with a meeting on March 8 of its Supreme People's Assembly. Its state media has been heralding the event and the role leader Kim will play.

It would be difficult for the North to launch one by the time of Kim's 67th birthday in Feb. 16. Another possible date is April 25, the anniversary of its Korea People's Army. (Editing by Jonathan Thatcher)