A top U.S. trade official said yesterday the Reagan administration is dissatisfied with Japan's latest proposal to open its markets to foreign imports and strongly hinted that the Japanese should alter their plan before Congress takes action on a series of protectionist bills next month.

In the administration's strongest response to the Japanese action plan announced this week, U.S. Trade Representative Clayton Yeutter said "there are both pleasant surprises and disappointments in the package."

Yeutter said he was disappointed that the Japanese still have refused to address some tariff and nontariff barriers, particularly the issue of government procurement of telecommunications products. Forest and citrus products are examples of other categories in which the United States would like to increase trade, Yeutter said.

The other disappointment was that many of the policy changes would not take effect until 1987 or 1988, Yeutter said. "To me, that's not very responsive in a good number of cases," he said. Yeutter said that in some instances the Japanese legislature, the Diet, would have to act, but some of the measures could be enacted promptly.

Yeutter, whose remarks followed a breakfast with the Republican Task Force on International Trade Policy, noted that when Congress returns from its August recess, it will begin debating numerous pieces of trade legislation largely aimed at Japan.

"There's another 30 days or more before that legislative activity will begin," Yeutter said. That time should "provide the opportunity for the government of Japan to be more precise" in the interpretation of its program and for "Japan to agree to a revised timetable" for implementing the program.

Yeutter said he didn't know if such a revision was feasible. "I hope the Japanese will consider an alteration of the timetable," Yeutter said. "It should be an opportunity for them to be more precise in product coverage and the precise meaning of these changes."

The Japanese action plan was an attempt to head off support for protectionist legislation building in Congress. The Japanese government this week approved a three-year market-opening plan that included the reform of 88 regulations about which foreign business people have complained.

Although the main points of the action program had been announced earlier, the Japanese government this week unveiled details of the plan. In addition, Prime Minister Yasuhiro Nakasone asked the Japanese people to "willingly accept foreign products."

Leading proponents of protectionist legislation in Congress greeted the action plan with skepticism, saying that Japan many times in the past has said it would open its markets but without result.

Sen. Frank H. Murkowski (R-Alaska), chairman of the Republican task force, said that when members of Congress return home during the August recess, "we're going to hear an awful lot about the growing trade imbalance." The Japanese plan "is too little and the timing involved in relief is too far away. . . . While it represents a start, it's just not enough."

The Reagan administration has maintained that it does not favor legislation aimed at curbing imports and would prefer negotiating with the Japanese. However, many members of Congress have said the administration has not been tough enough and that legislation would force the Japanese to act.

"Congress is really no more protectionist than it has been in the past year," Yeutter said. "It is frustrated, frustrated with a $150 billion trade deficit and bilateral deficits with individual countries like Japan." The trade deficit with Japan last year was $37 billion and so far this year it is running at an annual rate of $54 billion.

Yeutter said he will be in Japan later this month to talk with trade officials and will make his disappointment known then. Yeutter also is expected to make a major trade policy address, which he particularly wanted to present in Japan because of the deepening trade problems with them.

Yeutter said he was pleased that Japan urged its citizens to buy more foreign goods. "That's a very positive element, assuming those steps are taken promptly," Yeutter said.

Another welcome move was the opening of Japan's financial markets, which should eventually result in the strengthening of the yen against the dollar. That would tend to increase the price of Japanese products relative to American-made goods.