Two years after the Clinton administration placed the program on a back burner, Congress is about to redouble U.S. efforts to build a national system against ballistic missile attack, putting it at odds with the White House and at risk of confrontation with the Kremlin.

Republicans leading the initiative stress their plan is not a return to the "Star Wars" dream of President Ronald Reagan, who envisioned a space-based shield that would make the United States impenetrable to a massive launch of enemy missiles. Rather, the stated aim now is to erect a more modest, ground-based system that would protect the country against accidental launch or limited attack at a time when more nations are coming into the possession of ballistic missiles.

But opponents regard even this scaled-back effort as dubious technologically and not urgent strategically since little immediate threat exists. They say the program is a waste of the billions of dollars that the House and Senate appear ready to pour into it over the next few years.

Moreover, administration officials worry that a hellbent congressional effort to develop a missile defense system, coupled with renewed Republican talk of undoing the 1972 Anti-Ballistic Missile (ABM) Treaty, will upset relations with Moscow and scuttle the planned elimination of thousands of nuclear warheads.

When the Senate returns from its August recess today, it is scheduled to debate a compromise measure hammered out by a four-man bipartisan group to avoid breaching the ABM Treaty while still calling for accelerated development of a national missile defense system.

In attempting to establish a policy that can be supported by a broad majority of senators, however, the measure effectively postpones the day of political reckoning between proponents and opponents of a national system and between Washington and Moscow.

The measure would direct the Pentagon to "develop for deployment" a multisite missile defense system capable of being operational by 2003. But the decision to deploy would be put off until an unspecified time and subjected to considerations of affordability, effectiveness, threat assessment and treaty implications.

"I am not opposed to having an option to deploy providing we don't move toward it in a hasty way," said Carl M. Levin (D-Mich.), a liberal whose involvement in negotiating the compromise was key. "What I strongly oppose is doing it in a way that would undermine the relationship with Russia and the whole planned dismantlement of nuclear weapons."

For the Republicans who won control of Congress last November, revival of the missile defense issue seemed at first a simple way of dramatizing their general appeal for a stronger defense, while also addressing their real concern about the growing number of rogue states with access to ballistic missiles.

The GOP's "Contract With America" called for faster deployment of a national missile defense system. Many Republicans have sought to frame the political debate around the fact that the United States has no system to fend off even a single incoming ballistic missile. Opinion polls show that most Americans are surprised to learn the country lacks such a system.

But wrangles over the continued relevance of the ABM Treaty have complicated the debate. So has a related dispute about where to draw the line between a national defense system, which is covered by the treaty, and increasingly powerful "theater" systems for guarding against shorter-range missile attack, which do not come under the treaty's purview.

The 23-year-old ABM pact was meant to block Washington and Moscow from building nationwide defenses against ballistic missile attack, on the premise that as long as each country is vulnerable to the other's nuclear arsenal, neither will attack the other. The accord allows each side to establish a single-site system with no more than 100 interceptor missiles.

Administration officials say the treaty remains a cornerstone of international arms control efforts and abrogating it would jeopardize plans to cut U.S. and Russian nuclear arsenals to 3,000 warheads and possibly fewer under strategic arms reduction treaties. Such arms control agreements, not antimissile weapons systems, offer the more reliable protection for U.S. interests, say missile defense skeptics.

"No one will reduce their strategic forces if there's a buildup in strategic defenses," said Spurgeon M. Keeny Jr., director of the Arms Control Association. "If we lose all of this for a system that might kill only a handful of missiles, it's madness. We'll soon find much of the Defense Department's procurement budget going into this Fortress America."

But some key Republican players have questioned the relevance of the ABM Treaty in today's security environment, arguing that Cold War logic does not hold in a world no longer dominated by U.S.-Soviet tensions and now menaced by less familiar adversaries.

"Frankly, we think the ABM Treaty has to be renegotiated, so I'm not too concerned about bumping up against it," said Sen. John Kyl (R-Ariz.). "We've pretty much established the need to revise it, so we might as well face up to that."

A month ago, Senate Republicans were backing language in the 1996 defense authorization bill that required deployment of a multisite missile defense system by 2003. Arguing that such a move would violate the ABM Treaty, Democrats prepared to filibuster and the Clinton administration threatened to veto the bill if it passed.

After nearly a week of intensive talks in early August, Sens. Levin, Sam Nunn (D-Ga.), John W. Warner (R-Va.) and William S. Cohen (R-Maine) offered a compromise substitute amendment -- expected to win floor approval this week -- that promises to avert a showdown with the White House for now and clear the way for passage of a defense authorization bill.

The measure reaffirms that U.S. policy is to act consistently with the ABM Treaty but also approves negotiations with the Russians on the admissibility of the planned U.S. system. If those talks fail, the amendment asserts, the United States can consider withdrawing from the treaty.

The House already has approved a 1996 defense bill calling for deployment "as soon as practical" of a national missile defense system, without specifying the number of sites. And both the House and Senate are proposing to add several hundred million dollars to the Clinton administration program in fiscal 1996 for work on a national missile defense system.

The Clinton administration is not opposed to developing a system capable of protecting U.S. territory. It budgeted nearly $400 million for 1996 to pursue technologies for a ground-based system, beefing up the program a bit in view of congressional interest to include a deployment contingency early next century.

But when it took office in 1993, the administration drastically reordered the priorities of the Pentagon's missile defense effort, shrinking work on a national system, renaming the supervising agency, and concentrating about 80 percent of the funds of what is now called the Ballistic Missile Defense Organization on fielding theater defense systems to protect U.S. troops in combat zones abroad.

The rationale for the shift was the belief that the spread of shorter-range ballistic missiles poses a more immediate threat than the possibility of hostile nations developing intercontinental missiles that can strike the United States.

Currently, more than 15 Third World nations have ballistic missiles and 77 have cruise missiles, according to U.S. intelligence reports. By contrast, only several former Soviet states and China possess missiles capable of reaching the continental United States, and the U.S. intelligence community sees no new country developing the capability to hit the United States with a long-range missile for the next decade.

Administration officials also contend the likelihood of accidental launch by Russia or China is decreasing due to the elimination of many nuclear warheads in the former Soviet states and more reliable command and control procedures for Russian and Chinese forces. Moreover, they argue that with rapid advances occurring in information technologies, premature deployment of a U.S. system would limit the technical options and risk saddling the United States with an overly costly and quickly outdated system.

Other critics of a national system note that the country has been trying off and on for several decades to build one, without much success. More than $38 billion went into Reagan's Star Wars program alone.

"People are talking as if we've never tried this before," said Stephen I. Schwartz, director of the Brookings Institution's U.S. Nuclear Weapons Cost Study Project. "We don't seem to learn from the fact that we spent a lot of money before and didn't get much for it."

But many Republican legislators worry the administration is underestimating how quickly the threat of ballistic missile attacks from rogue countries may materialize. They cite development of North Korea's Taepo Dong-2 missile, capable of reaching Alaska or parts of Hawaii, and the potential sale to Third World countries of Russia's SS-25 as a space launch vehicle.

In fact, the U.S. intelligence community has been slow to provide a current estimate of the emerging missile threat to the United States. Lt. Gen. Malcolm O'Neill, who heads the Pentagon's Ballistic Missile Defense Organization, said in an interview that he has been waiting more than eight months for an update measuring the degree of uncertainty in the U.S. prediction.

Advocates of a national system, mindful of past failures to achieve their dream, contend the technology is now within reach.

"This is not Star Wars, this is not an umbrella system," asserted Warner, the Virginia senator. "This is a bare-bones effort to build a system to intercept missiles launched accidentally or in limited number."

Some of the more hawkish proponents still argue for a more ambitious setup, criticizing the Pentagon's current focus on ground-based interceptors. A study earlier this year by the Heritage Foundation, a conservative think tank, recommended concentrating instead on a Navy plan to deploy ship-based interceptors within three to four years, and then move to a space-based system by early in the next decade.

One area in which Republicans and Democrats generally agree is on the need for effective theater missile defense systems, with the GOP eager to add even more money to development efforts there as well. But the growing sophistication of theater systems is posing an ABM Treaty problem.

Some of the theater systems under development by the Pentagon may prove powerful enough to thwart ballistic missiles, meaning the Russians may view them as a national defense system and thus a circumvention of the ABM Treaty.

Administration efforts to negotiate with Moscow a distinction between defenses against long-range strategic missiles and short-range theater missiles have drawn Republican concern that the administration may be willing to accept too many limits on development of theater defenses, particularly on the speed of interceptors.

Accusing the administration of trying to apply the ABM Treaty to theater systems, Senate Republicans originally moved to include in the 1996 defense bill a unilateral declaration of the dividing line between strategic and theater weapons and a ban on the president negotiating any other demarcation. Administration officials protested that a unilateral interpretation of the demarcation line was unwarranted because the ABM Treaty is not constraining theater programs, and unwise because enactment would threaten ratification of the second Strategic Arms Reduction Treaty and set a dangerous precedent.

The Senate compromise includes a nonbinding "sense of Congress" provision reasserting what has been the demarcation standard, which would exempt the Pentagon's fastest, longest-range theater antimissile systems from ABM coverage as long as they were not tested against a missile with a range greater than 3,500 kilometers (or about 2,174 miles) or a velocity greater than 5 kilometers (about 3 miles) per second. But the measure also would permit the president to negotiate an alternative demarcation line between strategic and theater missiles, provided he sought congressional ratification of any new agreement with Moscow -- a condition the administration has been reluctant to accept. CAPTION: COMBATING THE MISSILE THREAT Two kinds of missile defense THEATER missile defenses are systems that can be transported abroad and are designed to protect troops in the field or warships in the ocean. These include an improved Patriot system, made famous during the Persian Gulf War; the THAAD, or Theater High Altitude Area Defense system; and the Aegis system for defending ships. The Clinton administration has placed a higher priority on developing and building these antimissile systems than on building a national system designed to protect the United States against missile attack. NATIONAL missile defenses are systems designed to protect U.S. territory against attack. A system under consideration would include a space-based sensor, ground-based radar, and ground-based interceptors that would destroy incoming missiles. The Republican majority in Congress has placed a higher priority on building this sort of system, at the risk of jeopardizing the Anti-Ballistic Missile (ABM) Treaty with Moscow. Spending Trends Clinton proposal: $400 million. GOP would add $300 million to $450 million to national missle defense. Total would rise to $700 million to $850 million. (This chart was not available) Countries that threaten With intercontinental ballistic missiles (which directly threaten U.S. mainland): Russia, China, Ukraine, Belarus With ballistic missiles (which don't have sufficient range to directly threaten U.S. mainland): Afghanistan, Bulgaria, Czech and Slovak republics, Egypt, Hungary, India, Iran, Iraq, Israel, Libya, North Korea, Pakistan, Poland, Romania, Saudi Arabia, South Korea, Syria, UAE, Vietnam, Yemen and some former Soviet republics. SOURCE: Department of Defense