Treasury Secretary W. Michael Blumenthal yesterday told an international audience that "we're not doing well in the fight against inflation" in the United States, estimating that the "underlying" or basic rate is now 7 percent.

The Carter administration for most of the past year had clung to an estimate that the "underlying" rate - stripping away abnormal food and energy costs - was 6 percent.

But in a speech to the Trilateral Commission, Bluementhal struck a somber note, even though he had earlier told reporters that "we'll see an abating of the (high) numbers of inflation in the summer and fall."

He discarded his estimate for reporters that the underlying rate is "6 1/2 to 7 percent - closer to 7 percent," and used only the higher figure in his formal remarks to the commission members.

The Trilateral Commission is a private group of influential leaders from Europe, Japan, and North America working to find solutions to international economic problems.

Bluementhal outlined the president's voluntary plan for a deceleration of wage and price increases, and predicted that the inflation problem would be discussed in detail at the economic summit in Bonn on July 16 and 17.

He said that the United States understood that an effort to control inflation is an "essential requirement for assuring the strength of the dollar."

He also pledged action on energy that would lead to a reduced dependence on oil imports, admitting "embarrassment" that more than a year has passed, without action, since President Carter proposed a program to Congress.