I was on my way to the galaxy radio quest when I met a Enclave soldier, they was kinda tough, seeing I'm low lvl with 10mm pistol and assault rifle. Well atleast I got a laser rifle

Do these spawn everywhere, even near Megaton?

http://fallout.wikia.com/wiki/Enclave_Soldier_%28Fallout_3%29

Near Dukov's place? I get him sometimes, too. You'll be more ready for them when they're supposed to come in.

Vengeance works a treat on them

Ha, last time I saw him I'd installed Impervious Power Armour, which adds a damage threshold back to PA, and was armed with a 10mm pistol. And he could run just as fast as me. That one didn't go well ._.

Yeah, if you have Broken Steel installed there's a glitch which causes a single Enclave soldier to spawn in certain locations.

Not a big deal, and if you manage to kill him, you'll get some nice loot early on.

Not near Dukov, it was on the west side of river, near some ruined house close to the Super-duper mart. Just NW of it.

According to Fallout Wikia enclave camps:
Super-Duper Mart
Northwest of Super-Duper Mart, half way to Springvale School, at the house with the silo.

It was prolly there.

He is one of the few remaining US army soldiers out there... Their training and equipment have suffered since they... Well, something funny just happened in their headquarters in Fallout 2... But they are still among the strongest fighters in the game, although they become rather easy prey later in the game.

i ran into the enclave at level 3, lucky part? they were friendly. so i decided to suround them with mines and shoot them afar with a sniper rifle. ahh, i even put one of there head chunks into a nearby pot.