Both @spicyness and @Tritium21 make excellent points but without joining the dots.
Lore needs privacy to communicate with the crystalline entity in order to tell it his plan. Killing Worf could have put the bridge crew on high alert that something was wrong.
Lore : Good, you understand perfectly so far. Next, I'll signal I'm about to transport something out at which time the
deflector shields will turn off for a moment, and if you move in
at that time...
Given that his plan is still based on deception (and since we know that Data and by extension, Lore could have killed Worf with a single punch) it follows that Lore must have had a good reason for not doing so. Echoing @spicyness' answer, if he had killed Worf, that would have shown up on the ship's bio-scanners had anyone on the Bridge thought to check them. All they know at this point is that Data(Lore) ordered an "emergency close" of the turbolifts.
He might even be planning to duplicate Worf's voice if anyone actually messages him but there's no way he can easily duplicate his lifesigns. If these aren't found, this would instantly scupper Lore's plan.
Also, shortly after tackling Worf we see Lore preparing to feed the crew to the Crystalline Entity. If Worf was dead, there would be one less meal for his friend.