Could it be

Missile

Reasons:

• Beloved of the moderates / A sometime worker hesitates.

You don't want to get totally involved into a war, nor not have any part in it, so you just shoot missiles.

• With many keys I am used wellOr waters fiery weapons quell.

ICBMs use plenty of missile keys to launch

• Or waters fiery weapons quell.

Missiles superseded the big fire-spewing guns in navies.

• An agent joined in retrograde.

I don't know. Maybe the self-destruct missile and Soviet Agent in Hunt for Red October

• Lose me, and you may be dismayed.

Umm, a missile may have many classified systems, so it would be very bad to loose one.

Could it be

Missile

Reasons:

• Beloved of the moderates / A sometime worker hesitates.

You don't want to get totally involved into a war, nor not have any part in it, so you just shoot missiles.

• With many keys I am used well

ICBMs use plenty of missile keys to launch

• Or waters fiery weapons quell.

Missiles superseded the big fire-spewing guns in navies.

• An agent joined in retrograde.

I don't know. Maybe the self-destruct missile and Soviet Agent in Hunt for Red October

• Lose me, and you may be dismayed.

Umm, a missile may have many classified systems, so it would be very bad to loose one.