Ford Motor Co. may have to increase the number of cars it imports if quotas on Japanese autos are not extended past their scheduled expiration date of March 31, the auto maker's incoming chairman, Donald E. Petersen, said today.

Removing the quotas now would cause serious harm to the U. S. economy, Petersen said in an interview. "When I think of the tremendous debate going on over the federal budget deficit and our enormous trade deficit with Japan, it seems to me that we'd be shooting ourselves in the foot if we supported removing these restraints from the Japanese at this time," Petersen said.

Japanese auto makers who sell cars in the United States have been operating under so-called voluntary quotas since April 1, 1981. The current limit on shipment of Japanese passenger cars to this country is 1.85 million a year.

The Reagan administration has yet to give a clear signal on whether it will support or oppose extending the quotas. But Petersen, who succeeds Philip Caldwell as Ford's chairman on Feb. 1, said that the administration should fight any efforts by the Japanese to end the quotas or to raise them substantially.

"Many people don't recognize that there is going to be a meaningful increase in the total volume of Japanese products sold in America because of an increase in the number of cars that the Japanese are assembling here," Petersen said en route to a gala Hollywood introduction of the Ford Taurus and Mercury Sable.

Japanese auto makers Honda, Nissan and Toyota already are building cars and trucks in the United States, and Mazda and Isuzu also have announced plans to assemble vehicles here.

South Korean auto maker Hyundai announced this week that it will introduce its Pony subcompact car into the U.S. market this year. The addition of the Pony -- of which Hyundai expects to sell 100,000 annually -- will increase competition in the small-car segment of the domestic market and will force U.S. auto makers to seek further reductions in their production costs, auto industry analysts say.

In response to those market pressures, Ford may have to follow the lead of General Motors Corp. and increase the numbers of cars it imports, Petersen said.

"Our first objective obviously is to keep our plants operating fully here. We're doing everything we can think of to move in that direction," Petersen said.

"We have to keep ourselves fully competitive," he said, adding that the need to import "will become a serious concern to us if we begin to see a complete land-open approach to this market at a time when no one has done a thing yet to change the valuation of the dollar versus the yen."

U.S. auto makers already have a $1,000- to $2,000-a-unit production cost disadvantage in comparison with their Japanese competitiors. Petersen said at least $1,000 of that is attributable to exchange-rate differences between the dollar and the yen.

"There's nothing we can do about that," he said of the currency differences. "But we think that we've been demonstrating that we've been working very, very hard to solve the problems we can influence -- namely, the quality of our products and the efficiency of our operations."

Since 1980, Ford has cut $4.5 billion annually from its operating costs, "and we are building a much more desirable, better-quality car," Petersen said. But the new Ford chairman, who spent his last five years as president of the company, said he does not believe that Washington is paying enough attention to the efforts of domestic auto makers to improve their position.

"There's a very strong strain in this particular administration to listen to classical economists," Petersen said. "They talk about the parity of free trade, which, of course, doesn't exist anywhere in the world. That is a very serious problem we have in dealing with Washington at this time."

Petersen, who was largely responsible for bringing out Ford's successful new line of aerodynamically styled cars, said that he will use his tenure as chairman to establish the company as the quality leader in the international auto industry. Petersen is 58 and is expected to remain in office until his 65th birthday.

"I hope that, as I get close to the end of my time as chairman, Ford Motor Co. will be acknowledged as the best quality auto producer in the world, bar none," Petersen said.