Oscar Pistorius' Blade Legs -- NOT Considered Weapons Behind Bars

Olympian Oscar Pistorius' carbon fiber blade legs could EASILY be used as a weapon behind bars -- but a rep for the South African prison where he's locked up tells TMZ, officials have decided not to confiscate the prosthetics.

The rep tells TMZ, Pistorius will be allowed to keep his legs ... at least until he faces a judge in a few hours -- at which point that decision might change.

Pistorius stands accused of murdering his girlfriend Reeva Steenkamp.

We're told SA prison officials typically confiscate any item that can be used as a weapon -- shivs, clubs, anything that can be filed down to a point (including hard plastics) -- but this is a special circumstance.

We called a few jails on this side of the Atlantic for good measure ... and we were told Pistorius would be lucky to keep his legs behind bars, especially if he were placed in gen pop ... where another inmate could potentially use Pistorius' legs to cause real damage.

Competitive advantage: Pistorius.