It's always a colorful scene on the day Kushiro's salmon-fishing boats leave port to open their season in the north Pacific. Children cheer and wave colored flags, wives blow kisses to sailor husbands, and the bright blue boats blow their horns as they leave the docks.

The ceremony was repeated last week, but with subdued enthusiasm because Kushiro, like other Japanese fishing ports, is feeling that pinch of tight new restrictions on the country's fishing industry.

In years past, 21 middle-sized drift-net boats sailed out to catch salmon; this year only 12 went out. Last year, said boat-owner Tetsuo Kitajima, his crew could sail out as far as 400 miles: This year they cannot go further than 200 miles.

He and his partners grossed $130,000 on the catch last year.This year he hopes it will be as much as $65,000. Things have gotten so bad, he said, that his son, Mitsuya, does not want to be a fisherman when he grows up.

The squeeze on fishing is the result of stiff restrictions demanded by Canada, the United States, the Soviet Union and other countries for fishing on the high seas. Last year, Japan had to accept lower catches because country after country, following the U.S. lead, cut down foreign fishing in their new 200-mile zones.

This year, Japan accepted restrictions on fishing in international waters in a series of negotiations regarded by Japanese as calamitous defeats. "We are now at the minimum and cannot step backwards any more," says Teruo Sasaki, director of the Japan Fisheries Association.

Here and in other fishing cities, the limits have drastic effects. Kushiro's mayor, Toshiyuki Wanibuchi, says his city's economy will suffer a 36 percent loss in direct income, increased unemployment and business losses for net-makers and other related industries.

Fish is still a staple in Japan's diet, providing half the average protein intake, and another round of sharp price increases is forecast. Last year, with the advent of 200-mile zones around the world, the cost of fish skyrocketed.Today, it costs about $3 to put four slices of salmon on the table; about a year ago, it was only $2.

The new restrictions imposed on Japan by foreign governments reflect a widely held view that Japanese fishermen greedily overfish in grounds around the globe and threaten world supplies. The leading fishing country in the world, Japan pulls in 10 million tons a year, only about 66 percent of which comes from its own coastal waters. The rest comes from grounds spread throughout the Pacific and some parts of the Atlantic.

Disputes over legal catches are endless. Japan is now feuding with South Korea over grounds in the Sea of Japan. New Zealand has ordered Japanese tuna boats out of its 200-mile zone until Japan begins importing more from New Zealand. So many Japanese fishing boats have strayed into Soviet waters that Kushiro's fishermen now are required to learn fundamental Russian language phrases to use when stopped on the seas.

In an agreement signed last month, the United States and Canada forced Japan to give up salmon and trout fishing in a large area of the north Pacific, claiming that many of the fish originate in Alaskan rivers. The Japanese calculate it will reduce their catches there this year by nearly 25 percent.

Japan then lost another negotiating battle with the Soviet Union and is excluded from another large swath of the northwestern Pacific in international waters. It means an overall cut of 32 percent in the salmon and trout catch this year and a loss of 80 percent of the highly valued red salmon.

To honor those agreements, Japan's government ordered a 36 percent reduction in the number of fishing boats plying the north Pacific grounds. In Kushiro and other ports, boat-owners participated in lotteries. They drew slips of paper and those who were unlucky had to keep their boats in harbor this year. Even the winners suffered because, under a cooperative agreement of all boat-owners, they must divide their earnings with those who lost.

The new restrictions have angered fishermen and boat-owners who argue that the Soviet Union, Canada and the United States have no right to curb their catches in international waters. They also are furious at their own government which, they believe, caved in unnecessarily to foreign pressures.

Mayor Wanibuchi protested to his government and to the Soviet Embassy in Tokyo and paid a call on the U.S. Consulate in Sapporo, pleading the case of Kushiro's fishermen and pointing out the potential economic damage. His visits were futile.

Boat-owners like Kitajima call the restrictions unfair. What right, he asks, does the United States have to limit catches in international waters?

"We have been told that the Americans permit seals to eat thousands of salmon each year," he says. "If that is true, it does not make sense to deny salmon to men.