It’s the kind of U.N. treaty you would expect - contradictory and unenforceable, one that would bind law-abiding nations while letting tyrants and terrorists off the hook. The Arms Trade Treaty currently being hammered out in Turtle Bay may well end up violating U.S. freedom and sovereignty, as well as common sense.

Negotiators at the U.N. expect to finalize a treaty by July 27. So far, we have only a “chairman’s draft paper” prepared by conference chairman Ambassador Roberto Garcia Moritan of Argentina. Its stated purpose is to establish “common international standards” for controlling and limiting the import, export and transfer of conventional arms, including small arms.

The draft provides a glimpse into what the final treaty might say - and what it says is fundamentally incoherent. On the one hand, it claims to uphold a nation’s right of self-defense. On the other, it calls on all nations, “without exception,” to limit arms transfers according to certain human rights criteria and whether they contribute to instability. In practice, Russia, Iran and China could use the self-defense clause to arm anyone, including Syria’s Bashar Assad. Meanwhile, they and others could invoke the human rights and anti-instability criteria to oppose U.S. arms sales to Israel, Taiwan, or others they consider objectionable.

The criteria that arms should not be used to “prolong” or “aggravate” instability is troubling. China could use such a provision to label U.S. arms sales to Taiwan as a violation of international law. In 1941, such a treaty would have made illegal the U.S. lend-lease program to aid Britain before Pearl Harbor.

The implication is absurd: If giving arms to an ally fighting a tyrant prolongs the conflict, the only “legal” option for the ally is to surrender.

Another problem is the draft’s invocation of “international human rights law.” Unfortunately, liberal activists often claim that strict gun control is a “human right.” This reference, then, could be interpreted in ways that infringe on Americans’ constitutional right to bear arms.

Why should we care what some U.N. treaty says? Just ignore it, you say, because our Constitution trumps everything. Well, not if the U.S. signs and the Senate ratifies it. At that point, the treaty carries the weight of U.S. domestic law.

Keep in mind that U.S. judges interpret the Constitution and the meaning of the Second Amendment. As the recent Obamacare decision showed, we never know what judges will say or how the treaty could influence them. Even if the president “signed” the treaty and the Senate refused to ratify it, gun control advocates and State Department transnationalist-leaning lawyers would argue that, under customary international law, the U.S. must implement the treaty’s restrictions lest we violate its “object and purpose.”

The draft’s human rights clauses could be misused in many ways to undercut U.S. interests. My Heritage Foundation colleague Ted Bromund notes that U.N. prohibitions on “conflict minerals” in cellphones were worked into the Dodd-Frank Act. With such precedent, imagine how the treaty could be used when guns, not phones, are at stake.

Other countries could use the treaty to boost their arms industries at our expense. Treaty language embracing European Union-blessed definitions of human rights and acceptable arms transfers could be used to protect their arms exporters from U.S. competition.

The administration may think it can take advantage of a treaty’s ambiguities, but the U.S. never does. Ours is a law-abiding nation. We try to live up to what we agree to. Besides, other countries won’t allow a double standard for us. They’ll insist that all aspects of the treaty - even those interpreted by anti-American U.N. bodies - apply to us. They’ll find willing allies within the U.S. who want to change our gun laws as eagerly as they do.

The bottom line: A U.N. Arms Trade Treaty will harm us while letting real offenders like Russia, Syria, and terrorists off the hook. Why on earth would we sign up to such a thing?

• Kim R. Holmes, a former assistant secretary of state, is a vice president at the Heritage Foundation (www.heritage.org).Follow him on Twitter @kimsmithholmes.