WASHINGTON (Reuters) - U.S. oil refiners are not conspiring to keep gasoline prices high and are not overcharging consumers for motor fuel, the industry's trade group told Congress on Thursday.

Under pressure to do something about soaring fuel costs, President George W. Bush has ordered federal regulators to investigate whether oil companies and refiners are collecting excessive profits from gasoline prices that top $3 a gallon in many parts of the country.

"Allegations of refiner price-fixing, price-gouging and other illegal pricing practices are patently false," Bob Slaughter, president of the National Petrochemicals and Refiners Association, said at a House committee hearing on gasoline costs.

Slaughter told the House Energy and Commerce Committee the refining industry had been subjected to dozens of investigations in recent years by federal and state agencies when gasoline supplies were tight, and in each case the industry was cleared of wrongdoing.

The Federal Trade Commission is scheduled to send Congress a report by next week on the agency's latest probe of high gasoline prices and possible refinery constraints. The report was mandated by Congress last year.

Red Cavaney, president of the American Petroleum Institute, also defended the business practices of its big member companies.

"We condemn price gouging," he told the committee.

The price of crude oil, which in the U.S. market was again above $70 a barrel, accounts for about half the cost of making gasoline.

"Oil companies do not set the price of crude oil," Cavaney said. "It is bought and sold in international markets, and the price paid for a barrel of crude oil reflects the market conditions of that day."

Strong global oil demand, especially from growing economies in China and India, and market concerns about possible future supply disruptions linked to the West's dispute with Iran's nuclear program, were helping to keep crude prices up.

High gasoline prices also reflect supply and demand realities as U.S. refiners are unable to meet the growing domestic appetite for petroleum products, Slaughter said.

He said "market volatility" that causes wide price swings would continue until fuel supplies increase. To get more supply on the market, he said, the permit process and other federal environmental regulations for building new refineries, or expanding existing facilities, should be eased.

There are 148 refineries currently operating in the United States that can process more than 17 million barrels of crude oil per day into gasoline and other petroleum products.

Companies are planning to expand refining capacity by 1.4 million bpd in the next few years, Slaughter said.