ST. LOUIS (AP) _ A barge loaded with 153,000 gallons of hydrochloric acid sprang a leak on the Mississippi River, sending up a cloud of hazardous vapor that drifted toward southwest Illinois, authorities said today.

Timothy W. Josiah, commander of the Marine Coast Guard's safety office in St. Louis, said no one had been evacuated, but that Illinois authorities moved in to keep people from approaching an area near where the Mississippi is joined by the Missouri River.

The Coast Guard advised all vessels to avoid the area, Josiah said.

Josiah said authorities believed that none of the acid had leaked into the river.

''That particular area along the shore has become a hazardous area,'' Josiah said. ''I don't expect this to become more than a localized problem.''

The leak began Wednesday night on the KAS-104, a barge owned by the Kenneth A. Steel Chemical Co. of Chicago.

Josiah said the vapor cloud was first noticed at 7 a.m. when it formed over the barge. The barge was cut away from a string of barges and moored by itself on the eastern shore of the river just above the Chain of Rocks Canal after the leak, he said.

He said the cloud first drifted west, and workers on a passing boat complained of burning eyes and other symptoms normally associated with an acid vapor. The wind then shifted to the east, he said, and the Coast Guard alerted the Illinois Environmental Protection Agency and the Madison County Civil Defense office.

The Coast Guard dumped 6,000 pounds of soda ash onto the deck of the 195- foot barge to neutralizes the acid, Josiah said.

The acid was stored in two cylindrical tanks mounted on the barge, Josiah said. Beneath the tanks are two hulls, he said, and the inner hull is coated with a special epoxy designed to prevent the acid from eating away the outer hull and leaking into the river.