The rationale was a familiar one, articulated by President Bush and senior aides frequently over the past two years as the administration has boosted spending on missile defenses and embarked on an aggressive plan to combat all kinds of missiles in all phases of flight.

But several administration officials said release of the 41/2-page statement, titled "National Policy on Ballistic Missile Defense," was intended to provide a more formal, comprehensive explanation for a set of weapons programs that consumes more than $8 billion a year and will likely top $9 billion in fiscal 2004.

The statement is essentially the directive Bush signed last year before announcing in December that he had ordered the deployment of an initial set of long-range missile interceptors in Alaska and California by September 2004. Known as National Security Presidential Directive 23, the text has been kept confidential for months as administration officials weighed when and how to release it.

Most presidential directives remain secret. But the missile defense paper was drafted as an unclassified document with the intention of offering it eventually as a public policy statement, officials said.

Its release coincides with congressional debate of the administration's 2004 military spending plan, including complaints from some Democrats that the deployment plan is too rushed and short on specific performance criteria. It also comes amid heightened U.S. concern about North Korea's pursuit of nuclear weapons. Among the chief reasons administration officials cite for stationing the first interceptors in the western United States and getting them in place is to counter a potential attack by North Korea.

But officials suggested yesterday that the timing of the release was largely because there was no other major news. In outlining the need for antimissile systems, the White House paper asserts that a growing missile threat from "hostile states" represents a "fundamentally different" set of circumstances than the United States faced during the Cold War standoff with the Soviet Union and "requires a different approach to deterrence and new tools for defense." It describes missile defenses not as "a replacement for an offensive response capability" but as "an added and critical dimension of contemporary deterrence."

The statement stresses that the national system set for deployment next year is only "a starting point" of what will be "an evolutionary approach" to better defenses over time. "The United States will not have a final, fixed missile defense architecture," the paper says.

It also puts special emphasis on using antimissile systems to defend "allies and friends" and includes a section promoting cooperation with Russia and other countries in developing and fielding missile defenses.