The latest contribution to the long-running debate over the feasibility of a comprehensive defense against Soviet ballistic missiles is a study prepared by a panel of the Defense Science Board, the senior scientific advisory group to the secretary of defense and the Joint Chiefs of Staff.

The secret report, completed two weeks ago, criticizes a Defense Department plan to begin elaborate demonstrations of ground- and space-based weapons for a missile defense system that could be deployed in the mid-1990s.

But the toughest remarks were removed from the report by the panel's chairman, Robert Everett, amidst allegations -- which he denied -- that the panel had buckled under Pentagon pressure.

The report was prepared to assist a formal review of the deployment plan by representatives of opposing Pentagon camps, including the Joint Chiefs of Staff, the three military branches and the department's senior political appointees.

A favorable outcome of the review, which concluded Wednesday, was considered crucial to the plan's success, but sources said yesterday that those involved had informally agreed that approval should be deferred until ongoing research produces more definitive results -- much as the defense science panel urged.

Besides Everett, a member of SDI's advisory panel and a former president of the MITRE Corp., the defense science panel included two retired Air Force generals, three weapons scientists, a former executive vice president of Hewlett-Packard Co., and former board chairmen from United Technologies Corp. and the Chevron Corp.

The report provides a glimpse of SDI's achievements and failings, as seen by some of those within the military community.

Following are selections from the report, beginning with some of the deleted material:

As a consequence of the current gaps in {SDI} system design and key technologies, there is presently no way of confidently assessing:

1. system performance against . . . requirements {of the Joint Chiefs of Staff},

2. system cost, or

3. schedule.

Therefore, the {SDI Organization, or SDIO} effort for next year or two should focus on filling these gaps. A . . . decision can be considered whenever sufficient progress is made to formulate with confidence a system concept.

There is a major need to create an adequate data base of the phenomenology involved in SDI. There is very little available information on how objects look in space or how rockets look in the boost phase. Component and system design are proceeding on the basis of assumptions and calculations which may or may not prove reliable.

The technology {to ensure} . . . the survivability of the {space-based weapons} is still uncertain. Vulnerability to attack by {Soviet ground-based antisatellite weapons} . . . and lasers during peacetime is particularly disturbing.

The design concept . . . is in an early stage and still quite sketchy . . . . It takes the form more of a list of components than of a consistent design.

None of the current cost estimates can be relied upon. They vary widely, even assuming that the current {deployment plan} . . . holds.

Funding requirements for the plans we have seen, however, exceed the {Pentagon's five-year budget plan} and greatly exceed the amounts presently under discussion in the Congress.

If necessary, the more expensive system demonstrations may have to be delayed in order to provide resources for such programs as gathering data on {Soviet} rocket plumes and on objects in space.

In view of the sketchy nature of the current system concept and the considerable uncertainty about congressional support and funding, existing schedule estimates are uncertain as well.

Plans for {orbiting a missile defense} . . . predict launch costs and launch rates which appear highly unlikely. We would urge a much more conservative approach.

The design of the organization . . . is still in an early stage . . . . The SDIO badly needs and does not yet have the support of a strong competent systems engineering organization without which we do not see how the enterprise can be managed.

On the other hand . . . much good work has already been done and plans are being made to begin to solve the problems. We strongly support continued work on SDI.

Military systems, particularly defensive systems, are never built in a single step and then left unmodified for a long period. Enemy reactions, new technology and changing requirements all lead to continual evolution. The plan to build SDI in phases is therefore reasonable and customary.

If a Strategic Defense System is deployed, we will in time have to withdraw from the ABM treaty. The point in the development process when such a withdrawal is necessary depends, of course, on the interpretation of the meaning of the treaty; the narrower the interpretation the sooner a withdrawal is required if progress is to continue.

The activities that must be carried out over the next couple of years, however, should not be seriously affected even if the United States adheres to the narrow interpretation.