Federation technology did include several personal Force Field type devices, the Arm Shield (109 Players Guide) and the Portable Force Field Generator (page 105 The Price of Freedom) for example, so the technology isn't unprecedented. I agree that you will inevitably begin a "escalation of force" and as TTK describes there are enterprising ways around Force Fields other then just over loading them with phaser fire. Also once phasers became less then optimal in any game I played in, players invariably switched to melee weapons (as Worf showed when fighting the Borg and using his Mek'Leth, or my favorite character, an Andorian Trachka dual wielding his Chaka using Chaka Hramdal style being a monster on the battle field). Phasers are also susceptible to Dampening fields, negating their use. Hence the TR-116 rifle being developed...
http://en.memory-alpha.org/wiki/TR-116_rifle
The ultimate progression would be a Borg style regenerative/adaptive shield design or some sort of personal Powered/Mechanized Battle Armour (that is shield equipped), but that is way out side of the bounds of what Star Trek usually portrays. TTK is also right in questioning the validity of regular Star Trek characters possessing or being issued with such devices like this. I would personally only allow Federation Marine, MACO or Hazard teams, Federation/Andorian Trachka [page 9 StarFleet Security Handbook], Federation Ranger units [page 3 StarFleet Security Handbook] or Federation Rapid Response Teams [page 3 StarFleet Security Handbook] to be issued with such devices.
I would also suggest you look into a suit called the Hazard suit (and Hazard teams), it is non cannon but still well with in the bounds of Federation Technology to develop and something I think would be a natural progression. Cannon is OK but IMHO it is when one steps outside of cannon that one truly starts to encounter the extraordinary.
http://memory-beta.wikia.com/wiki/Hazard_suit
A Hazard suit equipped with a regenerative/adaptive force field would be a kick ass suit, suitable for any type of front line Federation MACO soldier.