WASHINGTON (AP) _ The United States and Japan kept up their war of words Wednesday over a recently signed trade agreement. U.S. officials said that they are prepared to impose tests of their own, barring a mutually acceptable method, to measure whether Japan's markets have been opened to Americans.

Deputy U.S. Trade Representative Charlene Barshefsky told Congress that ''We have made it very clear where we cannot agree, the United States will, if it must, unilaterally apply indicators.''

Barshefsky's comments at a House Foreign Affairs subcommittee hearing marked the first time the U.S. side has publicly stated that it will select and impose its own numerical targets if it cannot reach agreement with the Japanese.

For their part, the Japanese have continued to insist that they will never agree to any types of targets for sales of American goods in Japan.

The negotiating framework announced by President Clinton earlier this month in Japan calls for establishing ''sets of objective criteria'' for measuring progress in opening Japan's markets in specific sectors.

But it will be up to the upcoming negotiations to settle on just what those ''criteria'' will be. Given the stance of both sides, it is likely that the forthcoming sector by sector discussions, which are expected to begin in September, will be every bit as contentious as the discussions that led up to the broad negotiating framework.

Various members of Congress pushed Barshefsky and Treasury Undersecretary Lawrence Summers and Under Secretary of State Joan Spero to explain why they believed the new agreement with Japan will be any more successful than previous agreements at reducing the trade imbalance between the two countries.

Summers told the panel that he believed the fact that the agreement commits the two countries to meetings every six months between the president and prime minister will serve to impose a strict timetable to various negotiations but he conceded that tough bargaining lay ahead.

''This is a foundation, but we have a lot more negotiating to do,'' Summers said.

However, various members of Congress said they had seen too many failed trade agreements with Japan to become overly optimistic about the results this time around.

They urged the administration to make clear to the Japanese that if the upcoming talks don't achieve measurable progress in reducing the U.S. trade deficit, then Congress would step in and pass laws to force the administration to impose trade sanctions.

''If you are not successful, you will see a coalition of Democrats and Republicans pushing for a Super 301,'' said Rep. Sam Gejdenson, D-Conn., referring to a former law that set specific timetables for retaliation against unfair trade barriers.

Summers and Barshefsky both assured the committee that the administration stood ready to retaliate by raising tariffs on Japanese products if the negotiations are unsuccessful.

''We are not reluctant warriors,'' Summers said. ''We are doing this because President Clinton believes opening markets is critical to our economic success.''