Iran and North Korea are at a tipping point, prepared to plunge ahead with nuclear programs and missile development that could lead to a cascade of nuclear proliferation across the planet, a commission report warned.

But if the United States erects a robust missile defense shield against a rogue-nation nuclear attack, that could limit the damage that such an attack could wreak on American cities, according to an interim report of the Congressional Commission on the Strategic Posture of the United States.

“Missile defenses appropriate to defend against a rogue nuclear nation could serve a damage-limiting and stabilizing role in the U.S. strategic posture, assuming such defenses are perceived as being effective enough to at least sow doubts in the minds of potential attackers that such an attack would succeed,” the report stated.

At the same time, if U.S. missile defenses are so extremely good that China or Russia might worry the American missile defense shield could neutralize their nuclear-tipped intercontinental ballistic missiles, that might prompt Beijing or Moscow to increase the nuclear threat directed toward the United States, the commission cautioned.

In other words, there might be such a thing as a U.S. multi-layered ballistic missile shield that could be too good.

The commission recommends that the incoming administration of President-elect Obama should enter talks with the Russians.

But Americans must take care not to negotiate a mutual reduction in American and Russian nuclear arsenals that would leave China an opening to increase its nuclear capabilities, “in an effort to compete with us,” the report warned.

China, flush with cash from U.S. consumers in a $230 billion annual trade imbalance in favor of Beijing, is well along in an immense military buildup that includes deploying new land-based intercontinental ballistic missiles (ICBMs) capable of striking targets in the United States, plus new nuclear-powered Jin Class submarines wielding nuclear-tipped missiles with a range of almost 5,000 miles.

In other words, a Chinese sub, hidden in an undersea voyage 2,000 miles from the U.S. west coast, could fire a missile and strike Washington, D.C., or New York City.

Iran has fired missiles in a salvo, fired a shorter-range missile from a submerged submarine, and unveiled plans for a space program that would involve much the same technology as ICBMs able to strike the United States.

Further, Iran refused world demands to cease producing nuclear materials.

The United States proposes building a European Missile Defense system to shield Europe and the United States from Iranian missiles.

North Korea has built nuclear weapons and tested one in an underground detonation, and also is developing the Taepo Dong-2 ICBM that could strike cities in the United States. Pyongyang also has launched a missile that arced over Japan before falling into the sea.

The United States, in response, has constructed the Ground-based Midcourse Defense system in Alaska and California to kill incoming long-range North Korean missiles.

“If Iran and North Korea proceed unchecked to build nuclear arsenals, there is a serious possibility of a cascade of proliferation following,” the report warned. “And as each new nuclear power is added, the probability of a terror group getting a nuclear bomb increases.”

Even if a terror group is unable to obtain a nuclear weapon or a nuclear-tipped missile from a nuclear state, a terror group could build a crude nuclear bomb, if the group can obtain fissile materials, the report continued.

Given all this, the United States has a need to maintain a credible nuclear deterrence, and reliable and safe nuclear stockpile, “for an indefinite future,” the report found.

To read the dozen-page interim commission report in full, please go to http://www.usip.org/strategic_posture/sprc_interim_report.pdf on the Web.