Automakers are showing little or no gain in fuel economy for the fifth straight year, with 1991 model cars having on average as much thirst at the gas pumps as they did in 1987, the government reported Tuesday.

The Environmental Protection Agency released the new fuel economy figures as the Senate considered legislation that would require sharp improvements in automobile fuel efficiency over the next decade.According to the EPA's annual fuel economy statistics covering about 1,000 cars, the 1991 models - both domestics and imports - show an overall average of 28.1 miles per gallon, slightly better than last year and identical to the fleet average in 1987.

While the most miserly cars such as the minicompact Geo Metro attain more than 50 mpg, more than half of the cars on the list achieved no better than 22 mpg. The increasingly popular passenger vans and specialty vehicles could on average do no better than the high teens.

The manufacturers want to "sell bigger engines, more muscle and acceleration which they call performance," said Joan Claybrook, president of Public Citizen, a Washington-based consumer organization, and a frequent critic of the automakers.

Auto industry executives have pointed to the significant improvements in fuel economy of cars since the 1970s, when the fleet average was only about 14 mpg, and attribute the more recent figures to consumer demand for larger and peppier cars.

Similar views are found in automobile showrooms.

"It's not the industry pushing performance. It's the consumer that's been demanding it in the last few years," said Ray Turk, a Nissan salesman in suburban Maryland.