U.S. defense officials indicated today they will urge Japan to increase military spending and expand protection for its ships at sea in light of recent Soviet military moves.

According to a senior defense official, U.S. Defense Secretary Harold Brown endorses the plans of Japanese military leaders that would require a large increase in defense spending during the next five years.

The official said Brown believes that because of Soviet moves Japan should "reassess and increase its defense spending over a period of time." He cited the Soviet invasion of Afghanistan and the recent buildup of Soviet forces on the Kurile Islands north of Japan.

Brown, who arrived here today from China, will tell Japanese leaders the invasion of Afghanistan requires increased strengthening of military capabilities of all industrial powers, including Japan, the official said.

It is rare for any U.S. official to encourage higher defense spending here because of Japan's sensitivity to any suggestion of a military buildup. In the past, American officials have encouraged Japan to modernize its forces but never have called publicly for an absolute increase in the proportion of Japan's gross national product that goes for defense.

Japan spends 0.9 percent of its GNP for defense and the figure of 1 percent has traditionaly been regarded as the upper limit politically tolerable in a country that officially renounces military force for offensive purposes.

The U.S. official noted today that the Japan Defense Agency hopes to increase that level by several tenths of a percent over the next five years and said this would be "quite suitable."

Secretary Brown's party arrived here today to brief Japanese leaders on his nine-day visit to China, where he and Chinese officials agreed to pursue closer military cooperation, including the transfer of American civilian technology that also could have military applications.

Japan has been increasingly worried about Soviet buildups in Asia, but it has planned no unusually large increases in its own defense arrangements. It took a special effort to get the administration of Prime Minister Masayoshi Ohira to maintain defense spending at 0.9 percent of the GNP.

Military leaders have wanted to increase that substantially, but the political leadership has been unwilling to go along in the face of certain hostile reactions from opposition parties.

Although endorsing the Japanese defense officials' goal the U.S. defense official said he was not urging this country to increase the size of its military force in such a way that it would appear to be a threat to the rest of Asia.

But he said Japan's forces should be modernized to expand antisubmarine forces and air defense systems and to expand the Navy's ability to provide escort with frigates and destroyers for Japan's merchant fleet, the ships that provide Japan's oil lifeline to the Middle East.

He said Japan should patrol a wider area of water around itself and do more to protect the sea lanes, although it should not think of trying to guard the shipping routes all the way in the Persian Gulf.

He said Japan should increase the payments it makes as part of the cost of keeping U.S. forces based in this country, but also observed that Japan has been steadily increasing its payment in recent years.

In past years, any large increase in Japan's military might was thought to be an alarming development for China and some Southeast Asian countries with long memories of the Japanese occupation during World War II.

But the official said that China now does not seemed concerned about Japan getting militarily more powerful and indicated that Brown had attempted to reinforce the new view during his talks with officials in Peking.

The defense official said that in talks with Japanese leaders Brown would stress that the Soviet invasion of Afghanistan creates a new situation in Asia, South Asia and around the world and that it will require concerted action among industrialized countries to see that the Soviets understand its gravity.