A national missile shield that would offer limited protection from attack by smaller, newly armed countries would cost almost $60 billion through 2015, the nonpartisan Congressional Budget Office says.

A CBO report released Tuesday said that's how much would be needed to defend the country from attack by a relatively small number of incoming ballistic missiles. It said those missiles could contain nuclear, biological or chemical weapons, capable of killing millions of people.

The report cautioned that many still believe hostile countries just developing long-range missiles, such as North Korea or Iran, could find easy ways to outmaneuver the proposed defense system.

Of the $60 billion price tag, Defense Secretary William Cohen told a Senate hearing Wednesday, "I have no way of knowing whether those numbers are accurate, or what they've included."

He said many items that would make up such a system were "open to resolution," including decisions on such items as how many satellites would be included.

Cohen said that he is prepared to make a recommendation to President Clinton this summer — the schedule the administration has set — on whether to commit toward deployment of a specific system.

"Do we have the technology? We have not resolved that issue yet," Cohen said. "We're close, but I think that the tests that are forthcoming will give us the ability to make that determination."

Senate Democratic leader Tom Daschle of South Dakota, who requested the report with Sens. Carl Levin, D-Mich., and Frank Lautenberg, D-N.J., said it made clear that the criteria of cost, operability, effect on national security and impact on arms reduction efforts can't be ignored in deciding whether to proceed.

"It is far too soon to evaluate the overall feasibility or advisability of the missile defense project," he said.

But Rep. Curt Weldon, R-Pa., a chief proponent of a missile defense system, said the CBO estimate was far too high and has "no basis in reality."

"You can't put a price on protecting American cities," Weldon said, but $60 billion was "totally out of line, out of synch with anything I've seen."

Congress last year passed by large majorities, and President Clinton signed, a bill stating it is the policy of the United States to deploy, as soon as technologically possible, a system capable of defending U.S. territory against limited ballistic missile attack.

The program has had problems with test failures and has met strong opposition from nuclear powers such as Russia and China. Russia says it would violate the 1972 Anti-Ballistic Missile Treaty and threatened to pull out of other arms-reduction pacts if the United States builds the system.

Clinton is to decide this fall, after another Pentagon test of the system in June, whether to continue with plans to have it operating by a target date of 2005.

The CBO said the first phase of a national missile defense would cost $29.5 billion through 2015, $3.9 billion more than the administration has estimated.

It would include locating 100 interceptors in central Alaska, constructing a high-resolution X-band radar and upgrading several existing early-warning radars.

The second phase, to be deployed by 2010 under current plans, would use satellites that could track not only powered-flight missiles but also missiles gliding through space. The third phase would add 150 interceptors, some at a second site currently planned for Grand Forks, N. D.

The administration has not yet estimated the cost of the last two phases. The CBO said the second phase would cost another $6.1 billion and the third phase $13.3 billion through 2015. It said another $10.6 billion would be needed for space-based sensors, satellites that share have other missions with support of missile defense.