A huge helium-filled balloon passed the halfway mark yesterday in its history-making expedition across the Pacific Ocean, with a buoyant crew reporting that despite bouts with rain, snow and ice, their only serious problem was one member's singing.

"They're threatening to throw Rocky Aoki overboard," Glenn Simoes, a spokesman for the venture, said yesterday. "He's singing Japanese songs and driving them crazy."

Aoki, 43, a veteran balloonist, owns the Benihana restaurant chain, which is underwriting the $250,000 expense of the first-ever balloon crossing of the 6,000-mile-wide Pacific.

The four-man crew lifted the 26-story-high Double Eagle V off from Nagashima, Japan, on Monday. The balloon is expected to reach land near Los Angeles early Friday morning.

However, the projections are subject to change because the balloon, which cannot be steered, is at the mercy of the weather and the winds.

Simoes said that two days into their journey the crew was in such good spirits and condition that they were talking about forgoing a landing in North America and continuing on to Europe.

"The primary objective is to cross the Pacific, but knowing these guys, they might just keep going," he said. "They're having the times of their lives."

The crew has food and oxygen to last 20 days, Simoes said. The decision on whether to continue on beyond the West Coast will be dictated by the weather.

The flight was orginally projected to reach North America today, but the journey was slowed when a series of storms 1,000 miles off the coast of Japan drove the balloon down to an inconveniently low altitude of 12,000 feet. The rains eventually iced over, adding an estimated 200 pounds to the gondola and polyethylene balloon.

By daybreak yesterday, the ice had melted off, but as the balloon traversed the ocean several hundred miles south of the Aleutian Islands, it ran into a minor snowstorm. Simoes said it was not causing any problems.

Last night's weather projections had the balloon picking up a slingshot effect from the trailing winds of a storm that was battering the coast of Oregon yesterday. If that occurs, the balloon will be thrust south southeast toward Los Angeles. If not, it is expected to hit the continent farther north.

The expedition is being led by Ben Abruzzo, 51, and Larry Newman, 34, both of Albuquerque, N.M., who were aboard the Double Eagle II that made the first transatlantic balloon crossing in 1978. The other crew member is Ron Clark, 41, also of Albuquerque.

The crew has elaborate radio equipment, and stays in regular contact with a private meteorology station in Denver. Crew members also have established voice contact with at least two passing jetliners.

The flight's altitude has ranged between 12,000 and 22,000 feet, and its speed has at times exceeded 100 miles per hour.