Total United States imports of heavyweight motorcycles were around 200,000 units in 1982, of which 80 percent were Japanese. Overall motorcycle imports run well over a million units a year.

Market analysts said that because of heavy backlogs of unsold motorcycles and extensive discounting, it was unlikely that prices would rise much in the current selling season as a result of the increased tariffs.

The International Trade Commission's specialists predicted that prices would rise about 10 percent in the first year of the five-year period for tariff relief the President ordered today -and another 12.5 percent in the second year. 'Escape Clause' Used

The President's order, which was signed in Santa Barbara, Calif., was taken under the so-called Escape Clause of the trade law authorizing help for industries severely hurt by import penetration.

It hewed closely to a recommendation by the United States International Trade Commission, which found last January that Harley-Davidson had been badly hurt by imports from four Japanese companies - Honda, Kawasaki, Suzuki and Yamaha.

Harley-Davidson, which had dominated the industry in the earlier postwar period, now makes only larger, more expensive motorcycles (over 1,000 cubic centimeters displacement).

But in earlier testimony to the I.T.C., the company said it hopes to reenter the market for machines of 750 cubic centimeters and thus needs protection there.