I beleive Martok (a Klingon) commands the joint Klingon/Federation Ninth fleet.
They probably operate like a real-world Naval fleet, with a command staff and a core of ships but heavily reinforced or stripped of resources as required by other theatres.
Currently the US fleets in the European area are reducing in size to support the US military's shift of focus to South-East Asia, but there will still be an Atlantic fleet and so on.
The Feds tactical fleets might even exist in peace time, but are so flexible that they are rarely mentioned. Admiral "Bitch" Nechayev for example might command the 2nd fleet that the Enterprise is nominally part of, but as Starfleet is very busy and spreads itself thin in peace time, the most we see in the TNG era is a small task group of ships in a few days reach, of 40 ships in BoBW, or 23 in Redemption.