The Patriot anti-missile defense system has been successful in the Gulf war. The Star Wars weapons proposed by the Strategic Defense Initiative are anti-missile weapons. Therefore, SDI will be successful. Right?

Wrong. This simplistic logical chain is being widely trumpeted these days, most recently in the pages of The Post by defense consultant Thomas Mahnken {"Lessons of the Gulf Missile War," op-ed, Jan. 29}. We can all be proud of the Patriot system. It is the kind of practical, workable anti-missile system we should be producing. But those who are trying to piggy-back their own pet programs on the back of this success story are sadly misinformed. Here are the facts about Patriot and SDI.

First, the Patriot program has nothing to do with SDI. It is funded and managed by the Army Air Defense Program Office and has not received a penny of the $23 billion Congress gave to SDI since 1984.

Second, the Patriot counters tactical ballistic missiles. These are the immediate threat our troops face. Despite congressional efforts over the years, SDI has refused to seriously address this problem. Rather it has spent almost all its time and money on trying to counter Soviet intercontinental ballistic missiles. Last year, the SDI program spent $130 million on tactical ballistic missile defense, out of a total budget of $3.8 billion. This year, the amount goes up to only $180 million out of $2.9 billion.

Third, shooting down intercontinental ballistic missiles is an extremely difficult, and as yet unsolved, problem. The Patriot evolved from an air defense system directed against airplanes to one capable of shooting down tactical ballistic missiles. Tactical missiles are short-range missiles about the size of a large truck and arrive on target at about 1 kilometer per second. We know we can shoot them down. ICBM warheads, on the other hand, span the oceans. They are about the size of a man, fly in four to five times faster, arrive in a barrage of up to 10 at a time and may be hidden among dozens of decoys. These we do not know how to shoot down with confidence.

Over the years, SDI has promoted one system after the other as an answer to this problem. All have been funded by Congress. None has worked -- not the X-ray Laser, the Alpha chemical laser, the Neutral Particle Beam Weapon, the Space Based Kinetic Kill Vehicle, the Space Based Interceptor nor now the latest, "Brilliant Pebbles."

To give some idea of the scope of the problem SDI faces compared with Patriot, consider that a battery of 32 Patriot missiles can defend an area of roughly 40 square miles. If this system were capable of shooting down long-range nuclear missiles, we would need more than 90,000 batteries with almost 3 million Patriot missiles to defend the territory of the United States. At present, there are total of 53 Patriot batteries in existence.

Fourth, defenses against the short-range tactical missiles are legal. A territorial defense against ICBMs -- even if one were technically possible -- would violate the 1972 Anti-Ballistic Missile Treaty signed by the United States and the Soviet Union. This treaty recognizes the still valid premise that trying to erect a shield against nuclear attack would only prompt the other side to increase the number of attacking missiles and devise ways to counter any defense. It is a no-win race.

Finally, there is the issue of cost. The Patriot program is not cheap. Congress has authorized $12 billion for this system to date. But that is peanuts compared with the $120 billion SDI officials estimated we would need to build, deploy and operate its so-called Phase I "Brilliant Pebbles" satellite system. This is a system of thousands of weapons satellites. The satellites would have very little if any capability to shoot down the low-flying Scud-type missiles that threaten our troops and the cities in the Middle East. To orbit this system, SDI officials said they would need to have annual budgets of more than $12 billion. The new downscaled version of SDI could still top $100 billion. With the many demanding needs we have to maintain and improve our conventional forces, plus the bills coming in from the Gulf war, it is difficult to justify this expense.

The Patriot is now a proven battlefield weapon. We should explore upgrading the system further to give it the ability to protect wider areas and interdict more capable tactical missiles. As for SDI, we should reorient the program much more toward developing follow-on systems to the Patriot, preserve its research on future technologies and abandon the unwise plans to orbit space-based weapons in violation of the ABM Treaty.

The writer is a Democratic representative from Florida and vice chairman of the House Armed Services Committee.