Nærforsvar relates to defence in the close proximity area - local defence is used in that context.

I came across a definition of harbour which reflects the meaning as well as some other documents, as seen below:
Def of harbo(u)r: A restricted body of water, an anchorage, or other limited coastal water area and its mineable water approaches, from which shipping operations are projected or supported. Generally, a harbor is part of a base, in which case the harbor defense force forms a component element of the base defense force established for the local defense of the base and its included harbor.

He had been elected as Mayor of Chester from 1634 to 1635 and during the Civil War and subsequent Siege of Chester, he was appointed as commander of the city’s local defense force in 1643.

In 1961 US Special Forces units began entering remote areas of Vietnam dominated by the Viet Cong. Their task was to organize local defense and strike forces aimed at stopping the enemy from gaining further control of such areas. The Green Berets set up fortified camps from which indigenous troops defended local villages and attacked and harassed the enemy.
(http://www.books-express.co.uk/book/9781841768397/Special-Fo...


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Note added at 2 hrs (2010-05-14 15:39:39 GMT)
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Oh no, I didn't see eodd's response before I put my response through.

Norwegian term (edited): nærforsvar

Local defence is all good and true, but nærforsvar has the additional meaning of defence at close quarters, as opposed to long-range artillery, mortars and missiles. The word local adds a 'close to home' undertone that is absent from nærforsvar.