The ballon DaVinci TransAmerica, in the most dangerous part of its flight across the United States, soared today to more than 16,000 feet over the Teton Mountains in western Wymoing and tonight was headed directly for the highest peaks of the Rocky Mountains near Denver.

The four crew members aboard the ballon were reported to be slightly giddy from wearing oxygen masks all day and growing tired from exposure to temperatures as low as 10 degrees.

Meterologists in Bedford, Mass., who are monitoring the flight by radio, said the craft, attempting the first non-stop balloon crossing of the United States, will have to remain at 16,000 feet or higher until it moves past Denver some time Friday morning.

Then it will descend to about 6,000 feet, picking up winds enabling it to make a left turn and move directly east.

Drifting along at 18 miles an hour in a light blue sky, the ballon flew just south of a 13,770-foot peak of the Grand Teton Mountains, a jagged, snow-covered rock that looms over the resort town of Jackson Hole. The craft flew over the Snake River and climbed the foothills of the Rockies where aspen trees flamed organe in the mountain autumn.

A project spokesman said the balloon, although flying south of it flight plan, was moving east at the edge of a fair weather system that would take it on to the Great Plains on Friday and that its chances of reaching the East Coast looked good.

The craft had traveled nearly 900 miles by sundown today from its liftoff Wednesday morning in Tillamook, Ore., on the Pacific coast.

Pilot Vera Simons of McLean, Va., who organized the much-delayed flight, and her crew of three were forced today to wear oxygen masks and stay at least 4,000 feet above the Rockies to escape lethal downdrafts that could send the 10-story-high balloon into an irreversible drop.

"We want them to get out of the mountains by the end of the day so they can come down [over] central Wyoming, take off their oxygen masks and warm up a little bit," said meteorologist Pete Leavitt.

Today the balloon looked like a silver toy to passengers aboard a chase plane that passed within several thousand feet to observe the crew's progress.

The original flight plan, which pilot Simons acknowledged was just an educated guess, called for a journey of 2,295 miles ending in 6 days and 9 hours in Norfolk.

The flight suffered a setback soon after lift-off Wednesday when crewmember and radio expert Dr. Fred Village, Kan., discovered that the craft's nine-radio communications setup didn't work properly.

Today the ballon crew, which had planned to maintain constant radio contact with reporters and CB radio buffs along the flight route, was able to make radio contact only over a radio telephone with the meteorologists in Massachusetts.

There was speculation today that a radio antenna on the ballon was damaged when it snagged on the gondola's rigging as the ballon was prepared for launch early Wednesday morning.

At the DaVinci's private weather service in Bedfore, Leavitt said today the crew members, frequently on oxygen, sounded a "little strange."

He said the altitude had made the balloonists "not as sharp, like having a couple of drinks" and that discussion of flight maneuvers for Friday were postponed until the ballon descends to lower altitudes over the Wyoming plains.

The gondola of the DaVinci is a 10-foot cube made of fiberglass and the crew members, when they stand on the gondola's upper level, are exposed to the weather. They all were reportedly growing exhausted today from the high altitude cold.

There are two beds on the gondola's lower level, and all four crew members reportedly slept briefly during the night as they flew over eastern Oregon.

The morning sun over Idaho earlier today warmed not only the crew but the more than 200,000 cubic feet of helium that keeps the 8,000-pound DaVinci in the sky. The sun's warmth forced the helum to expand, creating more lift and pulling the gondola upward several thousand feet.

The two materials that must be ocnserved aboard the ballon are the helium and ballast -- 5,000 pounds of water and sand. By dropping ballast or venting helium the balloon can navigate, moving up or down to catch winds that blow in different directions at different altitudes.

Before lift-off this week Simons said her job as a pilot is to be nigardly with helium and ballast, making sure that there are enough of both available throughout the flight for the balloon to keep moving east.

Simons' performance so far in the flight, according to the meteorologists, has been masterly. Only a tiny amount of helium had been vented by today and just 386 pounds of ballast has been dropped.

If these numbers remain low, the meteorologists said, the DaVinci's chances of flying across the country are excellent -- provided the wind keeps blowing east.