The snows and bitter cold of the Midwest's worst winter in decades is bringing new misery in the spring.

Floods caused by the sudden melting of the winter's heavy snowfalls have forced the evacuation of more than 15,000 persons in Ohio, Michigan and Indiana and led to the drowning deaths of six others, according to estimates compiled by the National Weather Service.

"The final act of this gruesome drama known as the winter of 1982 will be a flood," the Fort Wayne Journal-Gazette newspaper grimly observed in an editorial earlier this week.

A reporter for the newspaper put it more succinctly: "We're waiting for the plague of locusts."

The most severe flooding has been in this industrial city, where three rivers converge downtown and the overflow from the St. Joseph, St. Mary's and Maumee rivers have turned the streets of Fort Wayne into canals. Carl O'Neal, Fort Wayne's transportation department director, estimated that about 15 percent of this city's 55 square miles was under water today as a result of the flooding that began on Saturday.

The worst may be yet to come. The Maumee and the St. Joseph were expected to crest today at 26.5 feet--11.5 feet above flood stage, which would exceed by about a half foot the record set in 1913 when this city experienced its most devastating flood.

More than 1,900 homes on the banks of the Maumee were ordered evacuated today, and officials said that when it was over it would be the kind of flood that, under the laws of probability, should occur only once every 200 years.

Tuesday morning the city said the situation had been "stabilized," but by Tuesday night Mayor Winfield Moses had ordered the evacuation of 4,000 more people from the area near the rivers' confluence.

"We are in a race with the river," he said at a press conference today. "We have 2,000 to 3,000 volunteers working on an eight to 10-mile stretch of the St. Joseph. The dikes are becoming saturated with water and at the worst, they could give way."

Greenish-brown floodwaters strained miles of sandbags, and officials fear the city could be cut into six mini-cities if the makeshift dikes burst.

"The real problem now is that dikes are becoming supersaturated with water," said Bruce Hetrick, an aide to Moses. "The more saturated they get, the more likely that something is going to break and water can come rushing in."

Officials were establishing command posts in each of the sectors, stocking up enough fuel, food and medical supplies to last four or five days.

Concerned that some of the sectors would be cut off from hospitals and central supply depots, they made plans to use helicopters for emergencies.

Weather service officials said a light rainfall and abnormally warm weather last week rapidly melted the heavy accumulations of snow to cause major flooding in northeast Indiana, southeast Michigan and northwest Ohio.

The Illinois River is in flood along its entire length, and there has been minor flooding in parts of Missouri, Illinois and Iowa. There have been three drowning deaths in Indiana thus far, two in Ohio and one in Michigan. A seventh person died of exposure after clinging to a tree for 11 hours.

President Reagan stopped here briefly Tuesday to inspect the flood damage on his way back to Washington from a trip through the South. For a few minutes he joined in to help volunteers placing sandbags on the banks of this city's third river, the St. Mary's.

Meanwhile, help was pouring in. The Indiana headquarters of Kroger supermarket asked what was needed most, then dispatched a truck to Fort Wayne laden with 12,000 loaves of fresh bread.