Directives

Both Starfleet and the Time Patrol have a Prime Directive of non-interference and a law to the same effect applies to James Blish's Okies. Poul Anderson's Galactic League Patrol has a different, and secret, Prime Directive:

"Under no circumstances whatsoever may the Patrol or any unit thereof kill an intelligent being." (Kinship With The Stars, New York, 1991, p. 225)

The first clause of Isaac Asimov's First Law of Robotics prevents robots from harming human beings whereas the League Patrol Prime Directive forbids Patrolmen, on pain of memory erasure and cashiering, from killing intelligent beings. There are several differences but also a strong parallelism. I think that Larry Niven's protectors, not morally obliged but genetically compelled to protect their blood-lines, are like biological Asimovian robots.

Similar to the League Prime Directive is a rule of James Blish's Service that the date of the death of a sentient being must never be mentioned in any Dirac broadcast. This is because the Service receives Dirac messages before they are sent and works to bring about the events that they describe. The Service is an Event Police as against a Thought Police but must not become an Assassins' Guild.

So far, I have summarized operating procedures of seven science fictional organizations and will refer below to an eighth. Thus:

Starfleet (Star Trek);
the Time Patrol (Anderson);
Okie cities and Earth police (Blish);
the Galactic League Patrol (Anderson);
US Robots and Mechanical Men Inc (Asimov);
the protectors (Niven);
the Service (Blish);
the Terran Empire (Anderson).

The League Patrol applies principles that Anderson did not agree with but he was prepared to consider alternative possibilities in science fiction. Although the League does not kill, it certainly does not mind causing others to. We are told that the League's tactics are:

reason;
bluff;
bribery;
blackmail;
fomenting revolution;
"...any means that came to hand." (p. 225)

In "Enough Rope," we see a guerilla war that the League has brought about. Anderson presents in few words several planetary environments with their inhabitants and social structures. Whereas his Terran Empire contends with telepathic Chereionites, the League interacts with telepathic Gryeionites.

20/5/13: I should also have mentioned Anderson's Stellar Union Coordination Service whose role is to prevent interstellar exploitation.

22/5/13: ...and his Commonalty,a service organization in another spiral arm.