Iran may be using upgraded Silkworms, defense experts say. SURPRISINGLY ACCURATE HITS

Iran is using its small stock of Silkworm missiles with deadly effectiveness. The Silkworm strike yesterday against a Kuwaiti offshore oil loading terminal follows two attacks last week in which the missiles hit tankers with pinpoint precision.

Military analysts here are speculating that Iran may have an improved version of a missile long thought powerful but inaccurate.

``This latest attack was a static target, but it still suggests they've got Silkworms with improved guidance systems,'' says a congressional military expert.

Even before the oil terminal was struck, Kuwait and other conservative Gulf nations were scrambling to upgrade their air defenses against the Silkworm threat.

The Kuwaiti Air Force is equipped with four batteries of US-made Improved Hawk air defense missiles. At least some of these Hawks are now thought be be deployed on islands in the Gulf, where they could intercept Silkworms fired from the nearby Faw peninsula in Iranian-occupied Iraq.

Reports from the region indicate that high-ranking US Central Command officers have traveled to the Gulf to discuss how to best use Hawks against Silkworms, as well as possible improvements to Kuwait's air defense system.

Last week Kuwait unsuccessfully fired two Soviet-made SA-7 missiles at a Silkworm that later hit a tanker. The SA-7s, small shoulder-fired weapons, would at best be a last-ditch defense against Silkworms.

Stinger missiles, a similar but more capable US weapon, would be better. Saudi Arabia, however, is the only US ally in the Gulf that has Stingers. Bahrain wants to buy some, but there is congressional opposition to the deal and the outcome is not certain.

Silkworms are a Chinese variant of the Styx, a Soviet missile first deployed more than 25 years ago. Similar to the buzz bombs of World War II, they carry more than 1,000 pounds of explosives and are guided to targets by their own small radar unit.

Before their successful strikes last week, their use by Iran had been marked mainly by futility. One previous Silkworm launched at Kuwait had landed harmlessly in the water. Another had fallen on the beach.

If called upon, the US Navy fleet in the Gulf should be able to shoot down Silkworms, US military analysts say.

Silkworm electronics are relatively simple, so the electronic countermeasure units on US warships should be able to confuse the missile and throw it off course. If that fails, most of the US ships carry guided missiles which should be able to shoot the slow-flying Silkworms down.

Still, the best way to get rid of the Silkworm threat would be to prevent them from ever being launched, Washington analysts say.

Though Silkworm launchers are mobile, once detected they would be fairly easy targets to hit. The question is, who will hit them?

If the US were to attack Silkworm sites at Faw, it would be tantamount to involving itself in the Iran-Iraq ground war. Such a strike would also strain the Navy's capability, as it would likely involve a long-range attack by warplanes based on the American carrier Ranger in the Arabian Sea.

There is, however, another nation that could easily attack Faw. Iraq could hit Silkworm sites with relative ease using helicopter gunships, says Brookings Institution analyst Thomas McNaugher.

Iraq receives financial assistance from Kuwait. In return, ``Why isn't Iraq taking out the Silkworms?'' Mr. McNaugher asks.