The United States has never surrendered its sovereignty to the United Nations...
The attorney whose role is to advise the Chief Executive on all legal issues, officially known as the White House Counsel, has publically insisted that Barack Obama needs no legal authority but his own in going forward with military action against Syrian President Bashir al-Assad, as reported by the news portal The Hill on Sept. 9, 2013.
Regardless of Obama's full court press on the Congress to give approval to his Syrian military incursion, White House Counsel Kathryn Ruemmler insists her boss can constitutionally launch a military strike against Syrian government forces without deference to applicable domestic or legally binding international law.
The chief lawyer reasoned that the president could strike because of the “important national interests” surrounding the use of chemical weapons, even without Congress or United Nations approval.
Ruemmler contended that while the Syria situation “may not fit under a traditionally recognized legal basis under international law,” it would nevertheless be “justified and legitimate.”
As the situation in Syria stands as of now, non-constitutionally approved "international law" is a moot point.
Unless followed by the strict criteria laid out in the United States Constitution, any given example of international law simply isn't worth the paper it's written on regarding applicability to American citizens.
In keeping with the genius of the Founding Fathers ensuring a system of checks and balances were built into the Constitution, any given American president cannot lawfully enter into binding international treaties without the specific approval of the people's elected representatives.
In the case of treaties, the elected representation in question would be the upper chamber of the Congress.
As stated in Article 2, section II of the Constitution:
He [the president] shall have Power, by and with the Advice and Consent of the Senate, to make Treaties, provided two thirds of the Senators present concur...
In layman's terms, the Constitution gives the Congress a say in the president's direction of foreign policy by requiring Senate consent, by a two-thirds vote, to any proposed treaty presented by the president before it may go into effect as legally binding upon the American citizenry.
Being a member state in the United Nation's has never legally entailed the United States surrendering its sovereignty to the world body.
As previously covered by Examiner.com on Sept. 6, 2013, during a G20 Summit press conference in St. Petersburg, Russia, Barack Obama stated that any chemical weapons inventory maintained by the Syrian leader fails to pose "an imminent direct threat to the United States."
Per the War Powers Act of 1973, unless there is a direct and imminent threat to the United States or its vital national interests, the current president must receive Congressional approval before any military incursion.