Iraq Launches 3rd Missile--but Not at Allied Forces : Military: Troops rush to battle stations as Soviet-made Scud-B is test-fired. Key targets are within its range.

Iraq launched a ballistic missile Friday for the second time in two days, sending U.S. troops to their battle stations in preparation for war. The flight path, however, did not threaten allied forces, and the alert was canceled 90 minutes later.

The Pentagon said the test-firing of a Soviet-made Scud-B missile was the third such launching this month. The missile was aimed away from U.S. and allied troops deployed in Saudi Arabia, officials said, and its flight path was entirely within Iraq’s borders.

Even so, American troops, who have been in a state of heightened alert since before Christmas, have treated each missile launching as though it were the first shot of an all-out war.

Here aboard the hospital ship Mercy, a 1,000-bed vessel anchored in the Persian Gulf, word of the firing was flashed from U.S. communications personnel in Bahrain to the bridge in a classified message.

The mate on watch passed it within seconds to the wardroom, where the master of the civilian-crewed ship, Dan O’Brien of Reno, and the commanding officer of the medical contingent, Navy Capt. Paul Barry of Buffalo, N.Y., were meeting.

Bells blasted through the corridors of the 900-foot-long vessel, and O’Brien told the sailors and merchant marines over the public address system: “A missile has been launched. This is not a drill. All personnel take your emergency stations. I say again, this is not a drill. Attention on board. A Scud missile has been launched.”

Sailors in firefighting suits trotted to their positions in the unlikely event that the Mercy--a converted tanker that once carried oil from the Mideast to the West under the name of the SS Worth--was the target. A group of journalists were issued gas masks. The flight deck was closed to non-emergency personnel. O’Brien ordered the ship’s engines warmed up in case it was necessary to slip anchor.

The Scud-B, with a range of 220 miles, is one of four types of missiles in Iraq’s arsenal. The others are short-range, Soviet-made Frogs and the Iraqi-produced Al Hussein and Al Abbas.

U.S. intelligence officers have reported that Iraq’s fixed missile launchers are stationed west of Baghdad, but the country also has a number of mobile launchers dispersed throughout Iraq and Kuwait.

Saudi cities and allied troop concentrations are within range of the missiles. Iraqi President Saddam Hussein has said that if the United States initiates hostilities, his first target will be Tel Aviv, Israel’s largest city.

Together with 2,700 artillery pieces--traditionally the most effective weapons against advancing troops--and 4,000 tanks, the estimated 200 missiles in Iraq’s arsenal would represent a formidable challenge to allied forces in the event of war. Iraq also has a network of heavily manned defensive fortifications rimmed by mine fields and other obstacles.

If war breaks out, U.S. commanders believe Iraq is likely to rely on the same tactics it used during its eight-year war with Iran: Attacking forces would be allowed to punch their way through sections of the defensive lines, but then would find themselves in “killing zones” where Iraq has massed artillery, mortars, rocket launchers and tanks buried up to their turrets.

Tens of thousands of Iranians died in these zones, many of them young boys who wore wooden keys to heaven around their necks.

In an attempt to prevent U.S. surveillance planes from pinpointing missile and weapons sites, Iraq has turned off some of the radar devices that guide its military systems, intelligence officers said. It also has virtually eliminated test-firing of its artillery.

Times staff writer Douglas Jehl, in Washington, contributed to this story.