WASHINGTON — American foreign policy stands on the brink of substantial belt-tightening. The mounting expenses of servicing the growing national debt, combined with the skyrocketing costs of Social Security and Medicare as the 78-million-strong baby-boom generation retires, will leave less money for American initiatives abroad.

As I argue in my new book "The Frugal Superpower: America's Global Leadership in a Cash-Strapped Era," the burden that these obligations will impose on Americans — in the form of higher taxes and fewer benefits — will weaken public support for the expansive international role that the United States has played since World War II.

This will change the world, and not for the better. American foreign policy, for all its shortcomings, has underpinned political stability around the world. How, then, should the U.S. adapt what it does abroad to minimize the damage to global security caused by its straitened circumstances? Here are three rules for a frugal superpower.