WASHINGTON (AP) - The Pentagon's experimental missile defense, already beset by high-profile test failures, must now deal with longer delays from the contractor building new rocket boosters. The setbacks could jeopardize the missile's readiness by the target date of 2005.

Pentagon spokesman Kenneth Bacon said Tuesday that Defense Secretary William Cohen is not ready to abandon the 2005 goal, but he conceded that delays in technical aspects of the project are growing.

``We have always admitted that this was a high-risk program and part of being high risk is the deployment date; whether we can meet the deployment date of 2005,'' Bacon told reporters. ``We will try our best.''

What has become apparent, one month after a highly publicized failure to shoot down a mock warhead in space, is that the Pentagon's lead contractor on national missile defense, Boeing Co., is facing even longer delays than previously acknowledged in building a booster for the new missile interceptor.

The new rocket booster is designed to carry into space, then release, a self-guiding ``kill vehicle'' that would maneuver in the path of an incoming warhead and destroy it by force of impact.

The new rocket would replace the old-generation rocket booster used in an embarrassingly failed anti-missile flight test last month. A 10-year-old electronic component failed to send a signal to release the ``kill vehicle'' from atop the rocket, and the ``kill vehicle'' never attempted to intercept its target. The $100 million test was a washout.

The new rocket poses one of several technical problems Cohen is weighing as he considers whether to recommend to President Clinton that he take initial steps toward deploying a national missile defense.

Cohen said Monday he is postponing his recommendation for several weeks, and Bacon said it probably would be made in early September.

Asked whether 2005 was now an unrealistic target, Bacon said Tuesday: ``That's exactly the type of question the secretary is considering now.''

It remains possible that even if Cohen were to decide to move back the 2005 target by a year or two, he could recommend that Clinton begin the first deployment steps now in order to ease the overall schedule crunch. The first step would be awarding contracts for construction of a new X-band radar on a remote island in the Aleutians off Alaska.

The new rocket had been eight months behind in development, and Bacon disclosed Tuesday that it is running an additional several months late. He said department officials are still calculating an exact timetable. It originally was to make its first solo flight - without the ``kill vehicle'' aboard - last April; then it was delayed until November 2000, and Bacon said a further delay until spring 2001 was now likely.

The new booster's first flight in conjunction with testing the overall missile defense system is officially scheduled for sometime in the first three months of 2001, although it probably will not be ready for at least another three months beyond that, officials said.

``The gap is getting longer,'' Bacon said, referring to schedule delays for the new rocket booster. ``It has slipped. The question is: Has it slipped by so much that it changes the schedule of the program. That question has not been answered.''

The possibility of delays in developing the rocket booster was suggested in a June report to Cohen by a group of independent advisers who reviewed technical progress in the missile defense program. Their report said the Pentagon faced ``stressing challenges'' to demonstrate in time for a 2005 deployment that the rocket booster - technically called a ground-based interceptor - would perform reliably.