EASTERN SAUDI ARABIA, JAN. 18 -- U.S. warplanes attacked 11 previously undetected mobile missile launchers in Iraq today, hitting at least six, including three loaded with missiles pointed toward Saudi Arabia, senior military officials said.

Stung by Iraqi Scud missile attacks against Israel and Saudi Arabia this morning, U.S. aircraft conducted a frenzied search for additional missile sites as American and allied aircraft continued to dump hundreds of tons of bombs and missiles on targets throughout Iraq and Kuwait. Dozens of other aerial raids were canceled because clouds obscured many target areas, field commanders reported today.

Senior military leaders, on the second day of their ferocious air war against Iraq and only hours after Iraqi missiles struck two Israeli cities, cautioned that many setbacks and surprises could lie ahead before Iraqi troops are dislodged from occupied Kuwait.

"We are only 36 hours into what is a campaign," Gen. H. Norman Schwarzkopf, commander of Operation Desert Storm, told reporters early today. "It is not Panama. It won't be over in a day -- it certainly won't. . . . The fog of war is present. The picture is not perfect."

Despite many demonstrations of extraordinary precision by an arsenal of high-technology weapons never before used in war, U.S. commanders began to report some of the other certainties of combat: the toll of downed aircraft rose to four American and four allied planes -- including an Italian jet -- and intelligence discrepancies left the military unsure of how many Iraqi Scud missiles remain hidden.

Schwarzkopf, making his first public appearance since hostilities began Thursday, compared the scrambling to locate the mobile launchers to "finding a needle in a haystack." The United States hopes to prevent another Iraqi missile attack on Israel that might draw the Jewish state into the war and possibly splinter the international coalition.

Details also emerged today on what apparently were the first naval engagements of the conflict. Pentagon officials said carrier-based aircraft are believed to have destroyed three Iraqi boats, including a 147-foot missile patrol boat that Iraq had confiscated from Kuwait. The boat had carried four Exocet anti-ship missiles when it was part of the Kuwaiti military, and was capable of carrying a crew of 35. The boat was believed sunk Thursday when a Navy fighter, returning from a mission, dropped two 500-pound bombs on it, a Pentagon official said.

A Navy A-6 fighter also sank a Soviet-built Zhuk patrol boat today. The 75-foot vessel was last seen smoking and taking on water, with its crew, believed to number about 17, taking to lifeboats, the official said. And an unidentified Navy ship lobbed two cluster bombs at an oil platform service ship that had fired an antiaircraft weapon. The vessel was believed damaged, but officials did not know how severely.

U.S. ground troops also suffered their first casualties of the conflict today. Two Marines and a Navy hospital corpsman were slightly injured by fire from a Kuwait-based Iraqi artillery battery before it was knocked out by Marine helicopters and Harrier AV-8B fighter jets, officials said. Marines based near the Saudi border town of Khafji also came under fire from about 25 Iraqi artillery rounds and 12 rockets today, but no casualties or damage was reported.

In more than 2,100 attack missions conducted over the past two days, B-52 and Stealth bombers and other attack aircraft have systematically bombarded command centers, airfields, missile sites, the presidential facilities of Iraqi leader Saddam Hussein and chemical and nuclear facilities -- all targets designed to prevent preemptive Iraqi strikes and disrupt efforts to counterattack, according to military officials.

Some of the fiercest pounding is now being directed against the elite Iraqi ground forces known as the Republican Guards, spread in an arc northwest of Kuwait. Marine F/A-18 Hornet fighter-bombers and other aircraft have been pummeling the troops, considered the backbone of the Iraqi military, with highly destructive cluster bombs, which are particularly effective in piercing tanks and armored vehicles.

"It has been a constant, continual bombing with no letup," said Col. Manfred Rietsch, commander of a Marine aircraft wing assigned to bombard the Republican Guard units, shortly after he sent a new wave of 40 aircraft roaring toward their target.

Bombers and other attack aircraft also were reported to be blasting front-line Iraqi infantry troops near the Kuwaiti border as other aircraft reportedly air-dropped thousands of propaganda brochures into infantry trenches in a psychological warfare effort designed to turn the loyalties and morale of Iraqi forces.

While Schwarzkopf and other military leaders have provided only a skeleton account of the events unfolding in the war, hundreds of interviews with field commanders, pilots and troops by teams of news media representatives and combat reporting pools scattered at bases and encampments across the Eastern Province of Saudi Arabia have provided some additional details of the fighting.

The war began when Air Force F-117 Stealth fighter-bombers slipped into the Iraqi capital under the cover of darkness early Thursday morning and targeted the telecommunications building, which housed all vital communications links for the Iraqi military, according to Air Force Col. Alton C. Whitley, commander of the 37th Tactical Fighter Wing, which includes the two squadrons of Stealth fighters deployed to the Middle East. Stealth fighters flew 30 bombing missions in the first hours of the war, Whitley said.

One Stealth pilot trained his sight on the antennas and microwave towers atop the 12-story building, then dropped a 2,000-pound laser-guided bomb. In a videotape of the attack shown by military officials today, the building disappeared in a blast of thick, black smoke as large chunks of debris shot hundreds of yards in every direction.

Seconds after the bomb blast, the air exploded in volleys of brilliant antiaircraft artillery fire. The Stealth, flying high above the gunfire, unleashed more bombs, targeting specific rooms of some buildings, needle-like towers atop key communications sites, underground military command centers and some of Saddam's facilities.

The videotape, shot by cameras mounted under the planes, showed that highly fortified buildings that could not be destroyed by a single bomb were pelted repeatedly with bombs that punched large holes in their concrete roofs and exploded into the targeted rooms below. Pilots, in many cases, had been provided precise intelligence that included the floor plans of hardened command centers, according to Whitley.

"You pick precisely which target you want," said Whitley. "You can want the men's room or you can want the ladies' room."

Meanwhile, aboard the battleship USS Wisconsin in the Persian Gulf, sailors launched some of the first cruise missiles to strike Iraq. At 1:40 a.m. Thursday, the first of about 196 Tomahawk cruise missiles that would be fired from ships in the gulf, Red Sea and Mediterranean exploded from its launcher in a cloud of smoke, seemed to hang precariously in the air for a few seconds, then rocketed toward Baghdad.

As the missiles were being fired, missile officer Lt. Guy W. Zanti was listening almost gleefully to radio news accounts of the assault on the Iraqi capital. "I heard the correspondents on the radio in Baghdad saying, 'I hear bombs, but I do not see any planes.' That's because there were no planes."

Across the Arabian Peninsula in the Red Sea, the aircraft carrier John F. Kennedy sent F-14 fighters, A-6 and A-7 bombers and other aircraft on 90 missions during a 24-hour period. The planes joined aircraft based on the carrier USS Saratoga in roaring into Baghdad and western Iraq, firing high-speed anti-radiation missiles at Iraqi surface-to-air missile sites, blasting aircraft runways and hangers and hitting Scud missile launchers.

Several F-14 Tomcat fighter pilots flying air cover for the bombers over Baghdad said the hail of antiaircraft artillery that rose from the ground was a tremendous distraction.

"Our attack delivery meant we had to dive into that stuff and it was really hard to keep my eyes and my concentration on what I was doing in the airplane," said 31-year-old Lt. Mike Walsh of Virginia Beach. "It really awed me. It was spectacular. There aren't enough 'wows' and 'gollys' to tell you what the light show looked like."

Other pilots experienced dramatically different reactions. Lt. John Klas, a 27-year-old A-7 bomber pilot, said the red light in his cockpit signaling that enemy missiles had locked onto his plane flashed so many times that he lost count. "The butterflies in my stomach never really went away. It felt like there were a dozen of them in there."

Another Kennedy-based pilot, who requested that he be identified only by his call signal, "Rake," said he flew his mission jittery, dry-mouthed and praying: "God, please don't let me screw this up. Let me get in here and do it right and get back in one piece."

Several Navy pilots said the Iraqi fighter pilots they encountered seemed disoriented and confused by the air assault. Pilots who flew a daytime strike against an airfield in southwestern Iraq said a group of Soviet-built Iraqi fighters remained at least 40 miles away during the attack and retreated each time the American planes advanced. Another group of Iraqi jet fighters zig-zagged between two sets of American aircraft attacking targets in western Iraq, pilots said.

"They acted as if they were overwhelmed by the numbers of aircraft coming toward them and they couldn't quite make up their mind which strike group to go after," said Cmdr. John Hardy, executive officer of a squadron of A-7 attack planes. "We expected them to have fighter aircraft more regimented, more uniform in their attack, but they were truly random."

Seven pilots and crew members on four American aircraft have been confirmed missing in action after their planes crashed, according to military officials. Iraqi military officials claimed to have captured at least one downed pilot, but American officials said they were unaware of any American prisoners.

U.S. military officials said today that members of the Kuwaiti resistance reported rescuing a Kuwaiti pilot who crashed inside Kuwait.

American Special Forces teams have been dispatched to Saudi Arabia to assist in rescuing pilots who survive crashes in enemy territory, according to military authorities.

U.S. airplanes have shot down at least 11 Iraqi aircraft, military officials said, but added that they are uncertain how many Iraqi aircraft have been disabled on the ground.

Meanwhile, as the air assaults continue, weapons loaders and pilots have scrawled girlfriends' names and jokes on the high-technology missiles and bombs clamped in their aircraft. "Sorry this Christmas present was late," read the notation on one missile. "So were mine, thanks to you."

Ground troops continued to move northward toward the Kuwaiti border in what observers took to be preparations for a ground assault. The 101st Airborne Division was moving north toward the border today in trucks and C-130 transport planes. Chalked on the sides of some trucks were "Baghdad or Bust" and "Wham, bam, thank you Saddam."

Correspondent Caryle Murphy in Riyadh, Saudi Arabia, and Bill McAllister in Washington contributed to this report.