While Conquest mode in Battlefield 3 supports 64 players, the new Team Deathmatch mode will only support 24. This limit will be on all three platforms, including the PC, Xbox 360 and PlayStation 3.
The Team Deathmatch maps will reportedly be smaller, and will lack vehicles as well, so the intensity will remain high. There is also speculation that the mode will have the 12 player teams split into three squads of 4 each.
UPDATE: 3 teams of 4 on each side is confirmed.