Ronald Reagan was hailed, honored and generally treated like a head of state today while Japanese leaders fondly recalled his Presidency as a time of fewer frictions over trade and other issues.

Mr. Reagan, with a silvery crew cut the only mark of his brain surgery early last month, arrived here Friday for a nine-day visit but waited until today to begin a brief two-day segment as an official guest of the Japanese Government.

The rest of his time in Japan, he and his wife, Nancy, will be guests of the Fujisankei Communications Group, a television and newspaper conglomerate, as they were until today. The group is paying Mr. Reagan's way here, along with a $2 million personal fee.

After resting over the weekend and presiding over a concert for 17,000 guests in Yokohama to raise money for his Presidential library, Mr. Reagan had lunch today with Emperor Akihito and Empress Michiko at the Akasaka Palace in Tokyo. This evening he attended a glittering dinner at the State Guest House with Prime Minister Toshiki Kaifu and three former Prime Ministers. Grateful for Aid