Pentagon slashes estimates of Strategic Defense Initiative first-phase deployment costs. `STAR WARS'

The Defense Department has slashed the cost estimate for a rudimentary ``star wars'' antimissile defensive system from $115 billion to $69 billion, the Pentagon announced yesterday. The department, in a prepared statement and in testimony by top officials at a congressional hearing, said the Defense Acquisition Board had completed an annual review of the program on Tuesday and approved a series of restructuring moves.

The announcement did not set a timetable for initial deployment of President Reagan's Strategic Defense Initiative (SDI), saying US leaders could make decisions in the early to mid-1990s ``contingent on adequate funding levels.''

Defense officials have said initial deployment of even a partial defense could not be made before the late 1990s.

Although the Reagan administration has pushed hard for research funding on the controversial program, known as star wars, Congress has made sharp spending cuts over the past three years, and critics have said major questions remain on whether such a defense system would work.

Although Reagan announced in 1983 he was starting a program he hoped would protect the American population from attack, experts now say any initial deployment would attempt to protect only some US ground-based missile sites from a limited or accidental attack.

The Defense Acquisition Board, a panel of experts headed by Defense Undersecretary for Acquisition Robert Costello, reports to the Pentagon leadership on research programs. The board met two days ago as part of its annual SDI review, the Pentagon said.

The board reduced the estimated initial cost of a simple system of space-based interceptors, small missiles which can be fired at attacking missiles, from $52 billion to $18 billion.

That savings, the Pentagon said, would reduce the first-phase deployment of a ground and space-based system of interceptors to an estimated total of $69 billion.

Asked if the cost-estimates might mean earlier initial deployment of any star-wars system, one defense official said:

``It is premature to discuss specific deployment schedules. The decision to deploy a strategic defense system will be made by future national leaders in the early to mid-1990s, contingent upon adequate funding levels.''

A study group headed by SDI Chief Scientist O'Dean Judd recommended modifications in the first-phase system to cut in half the number of small defensive missiles, known as ``smart rocks'' based in space and at the same time increasing by 70 percent the number of interceptor missiles based on the ground.

The Pentagon said Defense Secretary Frank Carlucci told the board to continue concentrating on space-based defense system but stressed that there had been no change in Reagan's orders to comply with the 1972 US-Soviet Antiballistic Missile Treaty.