Sorry, my friend, but I cannot sign your petition. But, because I feel you are sincere and that you mean well I will tell you why.
The President cannot ORDER the release of classified information. Nor can Congress. Only a Federal Judge can do that (you've heard about the Separation of Powers, I'm sure) for this information that we all WANT...the REAL TRUTH about the UFOs and all it would probably end up going to the Supreme Court (assuming they would agree to hear the case) at which point those Agencies that hold classified information about UFOs would provide affadavits to the Court giving reasons why the information should not released.
Now, if the aforementioned Agencies (FBI, CIA, NSA, and so on) can make a convincing case that the release of this still classified information would pose a serious threat to the security of the United States the Court would dismiss the case.
And these Agencies are expert at convincing judges of just that.
You should hear Stanton T. Friedman on the subject sometime.
Now what you might try is petiti0oning the President and the Attorney General to appoint a panel of experts with high security clearance to look into the matter, examine the files, and see if THEY can agree as to the release of ANY of them.
I'd sign that.