The Bush administration wants to greatly expand the number and kinds of testing it believes is needed to build effective missile defenses, and is willing to spend billions more to do it.

In a sense, military planners have gone back to the drawing board to fulfill President Bush's goal of creating a reliable defense against ballistic missile attack on the United States, its allies and U.S. forces abroad.

The Bush administration sees no less urgency in obtaining a missile defense capability. But after months of reviewing options and studying the Clinton administration's approach, the Pentagon has decided to explore a wider range of technologies before deciding when the system could be ready for use.

"The focus of missile defense is no longer on deployment," says Lt. Col. Rick Lehner, a spokesman for the Ballistic Missile Defense Organization, which manages the Pentagon's missile defense work.

The focus is on testing, and lots of it. "It is going to be structured and disciplined," Lehner said.

It is also going to be expensive.

Intercept tests conducted during the Clinton administration cost about $100 million apiece. The Bush administration envisions more elaborate and more frequent tests.

The proposed 2002 defense budget submitted to Congress on June 27 provides $8.3 billion for missile defense, a nearly 40 percent increase over the current budget. It would be expected to take tens of billions more before a system is ready for use, although the administration has provided no firm figure.

For starters, the Pentagon is piecing together a plan to create a Pacific "test bed" -- a collection of test ranges from Fort Greeley and Kodiak Island in Alaska to Vandenberg Air Force Base, Calif., to Kwajalein Atoll in the Marshall Islands -- to pursue more realistic missile intercept tests.

Up to now, the only flight tests of interceptors designed to shoot down long-range missiles have involved launching an unarmed target missile from Vandenberg and trying to hit it with an interceptor launched from Kwajalein.

Just such a test is scheduled for July 14 -- the first intercept attempt in 12 months. Last July's attempt failed, and several weeks later President Clinton announced that the technology was not sufficiently mature to go ahead with deploying missile defenses.

Clinton was operating under a congressional requirement that he deploy a missile defense as soon as it was technologically feasible.

His administration chose to focus the bulk of its missile defense effort on a ground-based interceptor designed to collide with a hostile missile outside the earth's atmosphere during the midcourse of its flight. It did so because that technology is more advanced than others, such as interceptors fired from ships or lasers fired from satellites or airplanes.

Defense Secretary Donald H. Rumsfeld has decided that the midcourse system alone is insufficient to provide global protection.

He wants to build a "layered" system -- a combination of missile defense weapons. Some would be designed to attack a ballistic missile in the boost phase of its flight while it is easiest to detect, others in the descent phase and still others in midcourse. Some of these anti-missile weapons would be based on land, others at sea, others possibly aboard aircraft.

"As we proceed in time, and technologies are proven or disproven, we narrow down heading toward a solution," the undersecretary of defense for acquisition, Pete Aldridge, told reporters late last month.

Lehner said the Pentagon is aiming for deployment sometime between 2004 and 2008, but it has not firm target date.

In its new approach, the Pentagon will not only pursue different combinations of missile defense technologies -- some well advanced, some largely untried -- but also test them in ways not done before.

For example, the Kodiak Launch Complex on Kodiak Island, about 250 miles south of Anchorage, Alaska, would be used to launch target missiles over the Pacific. Kodiak also would have interceptors for test flights against target missiles launched from Vandenberg in California toward Kwajalein.

The Pentagon also would use Fort Greeley, about 100 miles southeast of Fairbanks, Alaska, as a site from which to launch ground-based interceptors at target missiles fired from an aircraft.

The government decided in 1995 to close Fort Greeley, but the 2001 defense supplemental bill before Congress now contains language permitting the secretary of defense to retain the base for missile defense purposes.

This more aggressive testing effort reflects Bush's determination to "set aside" the Anti-Ballistic Missile Treaty, which forbids the testing of missile defense weaponry from other than fixed points on land. Thus the Kwajalein-to-Vandenberg approach is allowed, but not testing from aircraft or ships.

Even more fundamentally, the ABM treaty bans any missile defense that is designed to protect an entire nation.

Having declared the ABM treaty a Cold War relic, the administration plans to go ahead with testing without regard to treaty limitations, although it has not yet said definitely that it will withdraw from the treaty. It hopes to persuade the Russians to either amend it or to replace it with a new "framework" in which the United States, its allies and Russia could pursue missile defenses cooperatively.

The treaty's limitations are not an immediate problem because testing of the kind that would violate the limits is not likely to be ready for another year or more.