Attorneys for ten major utilities engaged in battle with Westinghouse Electric Co. over its abandonment of long-term uranium supply contracts today began presenting evidence in their case here in U.S. District Court.

The first utility to offer evidence in the complicated trial was Florida Electric and Power Co., which signed the first contract in which Westinghouse agreed to provide a utility with uranium in connection with the sale of its nuclear reactors.

Uranium is the raw material which fuels the nuclear power plants utilities operate. Florida Power and Light contends it is owed 3.5 million pounds of uranium under the contract it signed in 1966.

Today, attorney for Virginia Electric and Power Co. are expected to put on their case. They are seeking to force Wedstinghouse to deliver almost 11.7 million pounds of uranium or pay more than $500 million in damages, about the price Vepco says it would take to buy the uranium at current market prices.

The utilities are asking that Westinghouse be forced to deliver uranium at the prices contracted for - between $8 and $12 a pound. Two years ago, Westinghouse told the utilities it could not fulfill the contracts.

Westinghouse contends it is excused from fulfilling the contracts under a section of the Uniform Commercial Code. That section excuses a breach of contract when unforeseeable events occur making fulfillment "commercially impracticable"

Westinghouse cites the Arab oil embargo, the existing of a worldwide uranium cartel, and various governmental actions as the unforeseen events that have pushed the price of uranium to more than $40 a pound.

Westinghouse counsel William R. Jentes told the courts that forcing Westinghouse to deliver the uranium at world prices would cost the company $2.2-to-$2.6 billion. "We can't stand $2.2 billion and we can't stand $2.6 billion, and everyone in this court-room knows it."

Lewis T. Booker, liason attorney for the various utilities, contended that Westinghouse had exaggerated the amount of loss it would suffer if forced to make good on the uranium portions of its contract.

Booker said Westinghouse's total loss, if it performs its contracts through 1993, would be $790 million, using the market rate of $26 a pound. That was the price of uranium at the time Westinghouse announced it would not fulfill the contracts.

The case is being heard without a jury by Judge Robert R. Merhige, Jr., who has suggested a number of times that he would like to see the parties settle their complaints instead of litigate them. The trial is expected to take up to six months. "I never expect to finish these cases," he told the lawyers at one point. "I expect them to be settled." Then he added. "I expect the Redskins to win the Super Bowl, Too."

Three utilities in the Pittsburgh area did settle out of court with Westinghouse in March after nearly four months of testimony was taken by Pennsylvania Judge I. Martin Wekselman.