there are nearly 17000 across the u.s
In the US, the executive branch has the power to enforce the law.
There are approximately 18,000 law enforcement agencies at the local, state and federal level.
Executive
Currently (September 2016) marijuana is illegal under US federal law, and it doesn't seem likely that changes to that law are imminent. So, at least in the US, it is NOT legal. Federal law trumps state law. (Federal agencies may choose not to aggressively enforce the law, especially in states where marijuana has been decriminalized, but that's a separate issue.)
Force bill
Currently (September 2016) marijuana is illegal under US federal law, and it doesn't seem likely that changes to that law are imminent. So, at least in the US, it is NOT legal. Federal law trumps state law. (Federal agencies may choose not to aggressively enforce the law, especially in states where marijuana has been decriminalized, but that's a separate issue.)
(in the US) There is no single pre-eminent, all-powerful, law enforcement body or agency in the United States. Therefore, it must be presumed that the question is asking about what federal agencies have nationwide police/law enforcement arrest powers to enforce CRIMINAL law ANYWHERE in the nation. I will omit attempting to list agencies and their agents who possess power to enforce CIVIL law as it wold apply to virtually EVERY federal agency within the executive branch. For the nationwide enforcement of CRIMINAL law - such a list might include (but is not limited to): the Federal Bureau of Investigation (FBI) - the US Secret Service - the US Marshall's Service - the US Park Police - Immigration and Customs Enforcement (ICE) - the US Border Patrol - the Bureau of Alcohol Tobacco and Firearms (ATF) - the US Postal Inspection Service - etc. This list is not all-inclusive and not all uniformed federal officers possess the same powers, even within the same agency (e.g.: Some Rangers of the US Forest Service are sworn law enforcement officers, but many are not). If another contributor can think of other agencies which qualify to be added to this list, their contribtuons are invited.
Force bill
how many advertising agencies exist?
(in the US) Law enforcement agencies are not even a part of the court system. Law enforcement agencies are part of the EXECUTIVE BRANCH of the government. The court system is part of the JUDICIAL BRANCH of government.
municipal agencies
that's how the mafia works