Citing the current gasoline crisis, the Carter administration yesterday rejected auto industry demands to weaken federal fuel efficiency standards for passenger cars in the early 1980s.

"I've got people all over this city in gas lines blocks long," Transportation Secretary Brock Adams said in announcing the government's decision. "We've got to maintain mobility in this country. We are in an energy crunch and it will continue." He said the nation will save 7.7 billion gallons of gasoline by sticking to the standards.

The administration decision came despite months of intensive lobbying by the auto industry to weaken the standards, including White House visits by the top executives of the three major automakers, Ford, General Motors and Chrysler. "They went everyplace in town," Adams said of the industry lobbyists.

The automakers told the Department of Transportation two years ago that they could meet the standards, which call for new car fleets to average 17.5 miles per gallon by 1985.

In recent months, however, industry lobbyists have attempted to persuade the administration that the cost of meeting the standards would be highly inflationary when reflected in new car costs.

Transportation Department officials said the White House was at least particially receptive to those arguments, because General Motors has been the largest and strongest supporter of the administration wage and price guidelines.

But ultimately Adams and Joan Claybrook administrator of the National Highway Traffic Safety Administration held firm. Supported by the current fuel crisis, the two officials were able to preserve the standards despite pressure from the White House and the Department of Commerce which had publicly supported industry arguments.

After yesterday's announcement, Assistant Commerce Secretary for Policy Jerry Jasinowski said "the decision shows that the Department of Transportation has no understanding of the capital, competitive and technological problems facing the auto industry. The problems the industry faces demand a more thorough and objective hearing."

The Transportation Department did make one minor concession, however. It agreed to lower the fuel economy standard from 18 mpg to 17.2 mpg for two wheel-drive light trucks in 1981. But Claybrook said that change was made after the department had studied new data and determined the change to be fair.

The fuel economy standards for automobile fleets, the average of all vehicles made by the manufacturer, require the following averages: 1981, 22 miles per gallon; 1982, 24 mpg; 1983, 26 mpg and 1984, 27 mpg. This year's fleets have a 19 mpg requirement. The standards were set in 1977.

General Motors and Ford had requested that those numbers be revised to: 1981, 21.5 mpg; 1982, 23 mpg; 1983, 24.5 mpg and 1984, 26 mpg.

But "after much deliberation," Adams said, "we have decided that the standards originally set by the department are the most equitable for the nation as a whole."

"We have to have vehicles that will run the greatest number of miles on a gallon of gas," Adams said. "This is one of the few ways we have to press American technology to give the consumer a break."

The automakers had argued that if they were given more time to reach the tougher standards, they could ultimately save consumers money through the use of more advanced technology.

But Claybrook responded yesterday by saying "our analysis of the information submitted by Ford and GM indicates that the increases in automobile prices because of industry compliance with the current standards will be more than offest by the overall savings to consumers from reduced gasoline consumption."

She said the nation's consumers will reap net benefits of between $500 million and $680 million over the life of their 1981-1984 vehicles because of the present standards. She said those figures were based upon "information supplied by Ford and GM."

Although the agency did reduce the requirements for two-wheel-drive light trucks (under 8,500 pounds), in response to a petition from the Chrysler Corp., it rejected another Chrysler proposal to lower the 15.5-mpg requirement for 1981 four-wheel drive trucks. CAPTION: Picture 1, BROCK ADAMS . . . "we've got to maintain mobility"; Picture 2, JOAN CLAYBROOK . . . cites consumer benefits