General Motors Corp. expects a 25 percent increase in its automobile exports this year, Chairman Thomas Murphy said yesterday.

Speaking to the National Press Club, Murphy said he expects GM's cars to be "very competitive" in foreign markets as a result of "downsizing" changes which have reduced the size and weight of the company cars.

Murphy also called on the government to reduce its budget deficit to help fight inflation, which he said is "the number one problem in America today."

Murphy said he was surprised and disappointed by the resignation Wednesday of United Auto Workers President Douglas Fraser from the administration's semiofficial Labor-Management Group.

Murphy, a member of that group, composed of 16 top business and labor executives who advise the White House on inflation and other economic problems, said that although the group "hasn't done anything earthshaking, it's been an effective instrument and I hope it will be continues."

Although Murphy would not specify GM's exact export plans, the company is planning a major export drive for the new smaller Chevrolet Nova. Last month, GM reportedly showed the Nova to 350 automobile dealers in Europe and Japan.

Murphy said GM's auto sales abroad increased 20 percent in 1977 and should continue to increase as "constraints of energy" make American cars smaller and more similar to foreign cars.American cars are now more and more "in consonance with what customers abroad want," he said. The reduced value of the dollar relative to other currencies also is making American cars a better buy abroad, Murphy added.

For the U.S. automobile industry as a whole, exports have increased this year. Commerce Department statistics show 59,582 cars exported to all countries except Canada in the first five months of 1978, compared with 52,807 cars in the first five months of 1977.

Imports, however, have also been increasing, to 1 million in the first five months of this year compared with 753,000 last year.

Murphy said GM is "trying to compete very aggressively with imports here." He said the Chevrolet Chevette is doing very well against foreign cars. "I hope we can influence the American customers to buy cars made here," he added.

"If we don't get inflation under control," Murphy said, "many of our markets will be taken over by foreign manufacturers." The government must "identify areas where spending should be reduced," he said, "and we the people ought to see that it is done."

Inflation is "a job for all of us," Murphy said, "and I think we have to get on with (fighting) it." He said GM is trying to do its part by keeping its prices down despite increased costs for the company.