Is the term 'law enforcer' acceptable? I don't see why it shouldn't be, but I haven't come across it, in contrast to 'law enforcement officers'. Of course, you can usually use 'the police', but it wouldn't include other state agencies like the national guard and so on. That's why I'm seeking some umbrella term, preferably the one that is less bulky than 'law enforcement officers'.
In parts of North America "Peace officer" is used https://en.wikipedia.org/wiki/Peace_Officer
That sounds very 1984 "Newspeak" to my British ears (although as noted in a comment, it was formally in use in the UK). In context the abbreviation LEO is sometimes used (but you should define it before using it, because it is not so well known)
The term "constable" can be used in British in a technical sense, as someone with the legal powers of a police officer even if they are not actually in the police. https://en.wikipedia.org/wiki/Constable#United_Kingdom
The word "officer" seems to be culturally important. The role isn't just "a person who enforces the law" but "a person holding an office that grants the special powers and responsiblities (for enforcing the law)". So most terms in English have the word "officer" in them.
The correct term is "law enforcement officer" if you need to include all those various non-police agencies that might not even have the legal postition of a constable, but may have an investigatory role.
In the Russian context there is a class of armed paramilitary groups that are termed Silovik. in an essay about Russian politics you should not translate, but borrow and explain.
A feature of Russian public life since Yeltin is the emergence of the siloviki or law enforcement and intelligence officers. The siloviki have control of many parts of the Russian state, and Putin himself is sometimes described as the lead silovik
Note the use of italics to typographically indicate the borrowed term.
It's a technically correct but not one you would hear or read normally. In other words, it's an uncommon usage. I am sure that native speakers would understand your meaning.
As you noted, the common terms include:
- law enforcement or law enforcement officer
- the police or a police officer
These terms are rather general and could include the local police department as well as county, state, and even federal law enforcement agencies although there are other more specific terms that might refer to non-local agencies:
- Sheriff or Sheriff's Deputy
- State Police or State Trooper
- Federal Marshall or Federal Agent