difference between 6346 and 6347?
 

I found that gnutella use following registered port at IANA.

gnutella-svc 6346/tcp gnutella-svc
gnutella-svc 6346/udp gnutella-svc
gnutella-rtr 6347/tcp gnutella-rtr
gnutella-rtr 6347/udp gnutella-rtr

what is difference between gnutella-svc and gnutella-rtr?

There is none IMHO? It uses only one port, which can be any you want (not only 634x). Also gnutella does not use UDP.

The settings in Mactella ask for 4 ports: Network, Upload, Push Request, and Client. The defaults are 6346, 6345, 6344, and 6300 respectively.

LimeWire also asks for 2 different ports: the Listening Port, default 6355, and the Force Local IP, default 6346.

So how many ports should I put in the router's NAT table for both servents to work properly? (not at the same time, of course) TIA

Just the port that you use for listening for incoming connections, which usually is 6346.
Remember to set in the the Gnutella client the public IP of the router, not the private LAN address that the computer running the Gnutella has.

Basically that's true, if the client does follow the Gnutella protocoll and uses only one port (e.g. TCP port 6346).
But I don't think that question is easy to answer, as long as we do not know what the purpose of those other ports is. I think the Unregistered misunderstood at least the meaning of the force_IP setting (which is no port number, but an IP-address used for sharing behind NAT routers/firewalls), actually Mactella describes various ports in the documentation. I asked the developers by email/PM and in their forum (Limewire, Mactella), got no answer.

gnutella uses one port, default is TCP 6346
 

A developer of Limewire answered, so they also use 6346 as default port (if that port is already in use LimeWire scans for a free port incrementally from 6346 to 6356). Only one TCP port is used for listening.

What is the purpose of Mactella's 4 ports, It's a miracle. The developers didn't answer.

Actually the difference between 6346 an 6347 is -1 :) I think you knew that already ;)