Japan's trade surplus fell to $7.45 billion in March, closing a fiscal year that saw the country record its first annual drop in six years, the Finance Ministry said Monday.

March marked the 11th straight time a monthly surplus was lower than it was during the corresponding period of the previous year.For March Japan's exports jumped by 17.4 percent compared with March 1987 to total $22.66 billion. Meanwhile, imports climbed 35 percent from the previous year to hit $15.2 billion.

Manufactured goods amounted to 47.6 percent of total imports in March, down a fraction from the 48.7 percent registered in February.

For all of fiscal year 1987, which ran from April 1, 1987, through March 31, exports rose 10.6 percent to a record $238 billion, while imports jumped 29.2 percent to total just under $162 billion, also a record.

The resulting $76 billion surplus in trade was down 15.3 percent or $13.7 billion from fiscal 1986, making it the first fall since fiscal 1981.

Ministry officials credited the climb in imports partly to improved markets for manufactured products, but mainly to rises in the price of imported oil.

Almost none of the drop in the surplus benefited the United States. Japan's surplus with the United States slid to just $50.85 billion for the 12 months ended March 31, compared with just under $52 billion the previous fiscal year.

Nevertheless, it was the first time since fiscal 1982 that the nation's exports to the United States were down on a year-to-year basis.

The trade figures are based on the value of all freight on board export vessels and the cost, insurance and freight value of all imported goods.

Japan's trade surplus with the European Community expanded to $20.1 billion in fiscal 1987 from the previous year's $18.2 billion. Japan's surplus with the Southeast Asian region increased to $14.8 billion compared with fiscal year 1986's $14.5 billion.

Ministry analysts said Japan's smaller trade surplus in fiscal 1987 would seem to indicate that the basic structure of the nation's external business is undergoing a drastic change stemming from coordinated efforts by the major industrialized countries to realign international exchange rates.

Another major factor, private analysts said, could be declining exports of Japanese automobiles. These shipments, which normally account for around 20 percent of the nation's overall exports, fell by 6.1 percent in volume in fiscal 1987 even as the value of those shipments rose an identical 6.1 percent.

Ministry authorities said this probably occurred because the rising value of the yen made Japanese autos more expensive.

Other product areas tended upward, the ministry said, especially in the automation equipment exports (mostly computers), which were up by 28.1 percent. Exports of electronic parts (particularly semiconductors) also were up, by 32.1 percent.

Ministry officials said the largest gain in the country's imports in fiscal 1987 was in crude oil and naptha - up by 29.2 percent over the previous year - and that imports of oil products in general soared by 65 percent in the 12-month term.

The authorities, however, said the share of manufactured goods in the country's overall imports increased to 45.6 percent in fiscal 1987 from the 44.1 percent figure of fiscal 1986.