I must to use Portals? If yes, it's possible to generate Portals in automatic manner in load model procedure?
Portals in jPCT are for geometry culling only. They won't help you in your case, there is no way to auto-generate them (because it's almost impossible to place them as good as an artist would be able to do it) and i don't recommend to use them. The code base they rely on hasn't been tested by anyone for ages now. Use octrees instead.
However, for A* use the grid approach that rolz mentioned. Paradroidz (albeit not using A*) is doing the same thing. It works grid based only (for AI, collision detection, movement) for entities that are invisible and uses a combination of grid/geometry based for entities that are. Works just fine.
Edit: Inspired by this thread, i've changed Paradroidz' path finding to a slightly modified A*...works better than before now.