The "common public interest" should not be limited to the US public. (even if it were, I'd argue that they are only mutually exclusive in the short term).
IMHO, the public should know everything its government is doing on its behalf. A more appropriate question would be how long the government is allowed to keep its secrets.
I don't dispute that there is definite realpolitik value in keeping secrets when trying to achieve short-term gains. However defaulting prevents that society in the future from determining if your actions were just when done in their name. Every time a politician acts in the name of myself and my fellow citizens, it reflects on me. On the other hand, I and my fellow citizens voted that person in to get things done on my behalf. The eventual publication of all governmental secrets keeps governments honest long term. After aboute ~10 years, a secret poorly received when made public after the fact no longer reflects poorly on the current officials in government (unless those responsible are still involved in government). What it does do is allow society to have a debate about whether they approve in hindsight of a government's actions.
If the government wants to keep a certain category of secret indefinitely, it should specifically ask the public if they acquiesce via a majority vote. A future public should be able to overturn that vote and make something public. Unilaterally affording government officials the right to make things secret indefinitely is a path to tyranny. The truth keeps governments honest.
Does such a policy put a country at a disadvantage when competing against adversaries without such a policy? Yes, it does, in the short term, since any governmental actor must consider the potential for fallout when their actions/policies enter the public domain. On the other hand, there are long term game theoretic advantages of holding your country to a higher standard. It establishes a basis upon which the population of other democratic countries judge their own government.
The US used to have this positive influence upon the World. There was a time when citizens of less free countries would look to the US and ask themselves, "Why can't my country be free like the US?". That question is no longer asked because we are no longer a guiding light for the world to follow, instead we've become the ship on the beach that has become the lighthouse to the sea.
Long-term, citizens the whole world over are going to be better off by establishing a precedence that everything their governments do in their name (from the local and state levels to the federal) will eventually become public.