Suppose I'm talking to my enemy. He's in front of me, I don't want attack him but I suppose he will do instead within few rounds...
If I lose initiative, having Combat Expertise +5 (without mention Improved Combat Expertise) is better than Total Defense.
This is precisely the case that I mention causes arguments.
In my opinion, you are in combat and can declare whatever wary sort of stance you like - even if initiative rolls haven't been made.
In the opinion of other DMs, the fact that you haven't thrown initiative means that you aren't in combat and can't declare actions that are in combat.
My counter is that as soon as you became aware of the enemy, and the enemy didn't immediately attack, the oppurtunity for surprise has been lost. Both parties are now effectively in combat - though both sides are basically declaring things like 'delay initiative' and 'hold action' while they engage in the important business of talking - and so long as both sides are wary and observing the other, neither side can get a jump on the other. Basically IMO your character and the enemy both rolled initiative some rounds ago, then both declared the intention to parley, and you are declaring something like, "I'm holding an attack defensively standard action, with the trigger of hostilities errupt and an enemy enters my threat zone, each round while negotiations continue or until I declare otherwise."
I've got no problem with that, though some DMs are much more anxious about getting their surprise round in and would make a big stink about that sort of ruling. In fact, some DMs are so testy about getting their surprise rounds in that they refuse to even let the players ask for an initiative check and combat resolution unless the players declare an attack action - basically forcing players to be sacrifices for their inevitable sudden betrayal as if that was cool or something. Blegh.
I will note that I'd interpret as a implied condition of this action, that you are basically standing their with your sword pointed at the enemy unless you have Quickdraw or similar ability. Otherwise, you are only holding the, "I draw my sword action." Being in a threatening stance like that could influence how the parlay proceeds for good or bad.