At least 32 people were believed killed today when a 608-foot freighter rammed a towering bridge over Tampa Bay, sending a Greyhound bus and several other vehicles plummeting 140 feet into the water.

All those known dead this afternoon were aboard the vehicles that fell into water when the bridge collapsed about 7:35 a.m., during a blinding thunder squall. No one aboard the freighter was injured.

One man whose pickup truck fell into the bay survived. Divers searched for additional vehicles and survivors during the afternoon, but Coast Guard Cmdr. Marshall Gilbert said there was little hope of finding anyone else alive.

Although authorities were unsure how many vehicles fell, drivers located the bus, three cars and the pickup by evening. The bridge was struck during the rush hour, but traffic was lighter than usual because of 35-knot winds and a driving rainstorm.

"There may have been others," Gilbert told reporters at a press conference. "The count could go higher."

Rescue efforts were interrupted during the morning by poor weather and by a 40-foot section of the bridge dangling precariously from what was left of the southbound span. Rescue efforts finally were halted late this afternoon and were expected to resume at daybreak Saturday. By the end of the day, 18 bodies had been recovered.

Twenty-three of the dead were riding a Greyhound bus bound for Miami. The driver was identified as 43-year-old Michael J. Curtin of Apollo Beach, Fla., and authorities were trying to identify other victims late today.

The only known survivor of the bridge collapse, 56-year-old Wesley MacIntyre of nearby Gulfport, was not seriously injured. He described the ordeal from a stretcher in the emergency room of St. Petersburg's St. Anthony's Hospital:

"It was raining very, very, hard," MacIntire said. "I was almost deciding not to go across the bridge, but I kept going. As I was approaching . . . the high part of the bridge, the whole bridge started to sway. Then when I looked, I could see the ship and the edge of the bridge was breaking off.

"I couldn't stop," he said. "I just slid and then I hit the ship and dropped into the water."

In the water, MacIntire held on to some debris from the bridge and called to the freighter for help. Crewmen dropped a rope ladder and pulled him aboard.

A doctor at St. Anthony's said MacIntire, who remained conscious throughout his ordeal, suffered headcuts, a sprained neck and swallowed some salt water. "It's miraculous, absolutely miraculous that he survived," Dr. Edgar Buren said. "His injuries are on the level of a common automobile accident."

The accident left a gap of more than 1,200 feet in the southbound span of the Sunshine Skyway bridge, the main route from St. Petersburg to Sarasota and points south. The bridge consists of separate northbound and southbound spans, each bearing two lanes of highway. The northbound span was not significantly damaged.

The vessel that rammed the bridge was the Liberian freighted Summit eNture. The feighter was on its way to pick up a load of phosphate at Tampa, the nation's seventh largest port. At the time of the accident, the Coast Guard said, "visability was zero."

The freighter knocked out the entire 800-foot steel center span of the southbound section and more than 400 feet of steel to the south of the center section.

Coast Guard officials said tonight that the ship apparently struck one of the bridge's steel and concrete support columns, glanced off and then hit another pair of pylons, shearing them off about 10 feet above the water.

Gilbert said part of the bridge fell on the bow of the Summit Venture, but injured no one.

After the wreck, the ship became stuck several hundred yards west of the bridge, unable to raise its anchor. Coast Guard officials speculated that the freighter dropped its anchor either shortly before or after the crash in an attempt to slow down.

Tugs were unable to free the freighter today, apparently because the ship's mechanism for raising its anchor had been damaged in the crash or because the anchor was entangled in bridge debris on the bay's bottom.

Today's collision was the second majar disaster at or near the Skyway in three months. On Jan. 28, 23 Coast Guardsmen were killed when the Coast Guard buoy tender Blackthorn collided with the oil tanker Capricorn. That accident occurred just west of the bridge, within several hundred yards of today's tragedy.

The Summit Venture was the third vessel to strike the bridge since the Capricorn-Blackthorn collisions, Gilbert offered no explanation for the accidents, saying simply, "It should not happen."

The Coast Guard announced that a Marine Board of Investigation would convene immediately to determine the cause of the accident and the National Transportation Safety Board dispatched investigators from Washington. Both agencies recently completed a lengthy inquiry into the Capricorn-Blackthorn collision but the results have not been released.

State officials examined the Skyway in February and pronounced it safe, Gilbert said.

One car on the bridge carrying four persons stopped 14 inches short of disaster.

"I figure the Lord was real good to the four of us," said a shaken Richard Hornbuckle, drive of the 1976 Buick. "As I came to the very top, I saw a black spot and hit the brakes . . . I didn't think I'd ever stop."

Hornbuckle, 60, and his three passengers scrambled to safety and rushed to wave off other vehicles approaching the wrecked part of the bridge.

The Skyway opened in 1954 with one bidge; the second span, which was severed today, was added in 1971. Authorities closed the bridge to traffic after the accident today, but hope to have safety inspections performed by Monday.