Eighteen months after President Reagan announced his "Star Wars" initiative, the administration remains so divided on its strategy and scope that the agency set up to run it plans to pay for outside help to define the program.

The Strategic Defense Initiative Organization (SDIO) has proposed a two-year, $6 million contract to corporations and research organizations to define the strategy, technology and systems needed for the program, which is supposed to destroy, possibly from space, missiles at any point after they are launched.

The bidders also are being asked to detail how their proposed systems could be expanded from near-term "limited defense applications" to "the ultimate goal of a thoroughly reliable defense against nuclear ballistic missiles of all reasonable ranges."

The only basic guidance the consultants are given is that the system must be able to "detect, identify, discriminate, intercept and destroy ballistic missiles" in their "boost" phase as they are launched, their "post-boost" phase as the missile is rising into the atmosphere, their "midcourse" phase as they travel through space and their "terminal" phase as the warheads streak down through the atmosphere to their targets.

It is not unusual for a Pentagon agency to contract for help in developing a weapon's concept or even a strategy for a family of weapons. But experts in the field said that a proposal as broad as this is highly unusual.

The contract has brought to the surface a debate inside and outside the administration over just what Star Wars ought to be.

One dispute is whether a first step should be to protect U.S and allied nuclear missiles before moving toward the more difficult task of protecting civilian populations. That appears to be the route laid out by SDIO's contract proposal, but a Pentagon official said "there has been no decision to move in any direction."

Critics, however, are arguing that protecting missiles first "forgets the president's goal," as one Pentagon consultant put it, because it makes missiles more important, not less, than people.

"It's as if they decided it's too difficult to defend people," another critic said. "So they decided we might as well defend ICBMs."

Some contractors are pushing to defend missiles first because, as one company representative said at a recent meeting, "Anybody knows you don't make money on technology research programs. We've got to have deployment."

Another issue is what countries are to be protected.

In his speech March 23, 1983, the president called on scientists to find "the means of rendering nuclear weapons impotent and obsolete" by destroying ballistic missiles "before they reached our own soil or that of our allies."

Last month, as part of its contract offer, SDIO declared these "allies" to be "all U.S. allies, not only the NATO countries."

"That's the whole world," one Defense Department consultant said.

A Pentagon official said that any system, even one protecting just the United States, designed to destroy missiles during the boost phase would have to be worldwide to cover all Soviet strategic missile launch points, including submarines anywhere at sea.

It is in the terminal phase that a system protecting U.S. allies would make a difference, he added, since that would require placing launchers on allied territory.

Although Reagan has made Star Wars a centerpiece of his defense and arms control policies, the shape of the program always has been vague.

After the 1983 speech, two presidential commissions made initial studies and reported that technologies were emerging that could make a total defense possible. Other studies, however, including one by Congress' Office of Technology Assessment, questioned the feasibility of any system, particularly one that has to destroy a Soviet land or sub-launched missile immediately after it was launched.

Today, the administration's strategic defense initiative (SDI) is a grouping of $1.3 billion worth of various agencies' research programs. All of them were under way at the time of the president's speech, from the Army's 12-year effort to develop an ABM system to the antisatellite laser research of the Pentagon's Advanced Projects Research Agency.

"There have been no new initiatives so far," an industry official familiar with the program said. "It's only a collection of disgruntled technologies."

The proposed SDIO contract calls for bidders to develop the "system architecture." One former top Pentagon officer said the contract will give Lt. Gen. James A. Abrahamson, SDIO's director, "some goals to set for engineers who want to build systems."

However, for defense contractors who are looking at SDI's proposed $26 billion in research contracts over the next five years, the SDIO offering is the key to future business. The agency plans to select 10 to 12 of them for the first phase, and then cut that back to less than half for a second phase, according to an SDIO spokesman.

The winners, sources said, would have an inside track on future contracts.

The contract, however, has been the focus of critical discussions both inside the Pentagon and at conferences around Washington featuring Abrahamson and other SDIO officials and attended by defense strategists and contractors.

Much of the talk, sources said, has been on defining the near-term goal as development and deployment of a system to protect nuclear missiles.

A system that protects missiles, one defense research company executive said, "does not lead to one that would protect populations." He explained that a system defending hardened missile silos would be effective if it stopped 50 percent of attacking warheads. But an ABM system for cities would have to knock down all of the incoming warheads, since only one or two could cause devastation.

"The Army," one top former Pentagon official said, "is pushing for a near-term ABM system because that's what they've been doing."

Without something practical to point to, one official said, the Star Wars program could lose its support in Congress.

"Near-term" missions, the SDIO contract proposal also says, include "defense of the allies and deployed U.S. forces against tactical ballistic missiles."

In answer to questions, SDIO said that by near-term it means "theater weapons," such as the Soviet SS20 medium-range nuclear missiles which are based in the eastern, central and western portions of the Soviet Union and therefore can reach targets in an arc from the Far East, through the Middle and Near East to North Africa and Western Europe. A Pentagon official said it could include Soviet SS12 missiles with shorter ranges.

A near-term requirement would require a Star Wars system that could protect such widely diverse countries as West Germany and England as well as Australia, Korea and Japan.

"We have told our non-NATO allies that if we develop the technical capability to destroy short-range systems, they will be deployed to cover all allies," a Pentagon official said.

About 230 requests have been received for the draft proposal and 30 of those have submitted questions, an SDIO spokesman said.

Because of the interest in the contracts, the closing date for bidders has been set back from Sept. 27 to Nov. 1.

The winning contractors will be given a classified analysis of the Soviet threat for both the short- and long-term and will have to design their systems.