Who is responsible?

It is always hard to know in Washington who's in charge. Currently the Treasury is faced with an annual deficit of around $200 billion; surely with a thundering gap like that the separate branches of the divided government will agree on a rescuing operation? Probably they will in time. In the meantime there's an interval in which things may get sorted out. Lacking clear-cut guidelines in this amorphous system political parties tend to decay; people don't bother to vote. (In the last presidential election only about 55 percent of those eligible to vote voted.)

This often adds a vague quality to Washington affairs. Who is responsible? For example the National Commission on Excellence in Education has just written an ''open letter'' to the American people.'' It says, in effect, that feckless management of the schools has produced a ''tide of mediocrity.''

''If an unfriendly foreign power had attempted to impose on America the mediocre educational performance that exists today,'' it says, ''we might well have viewed it as an act of war.''

This is strong stuff; it bears on many other problems in Washington: who takes responsibility for guidance in national matters? President Reagan praises the new report and urges that the state and local governments promptly look into it. This involves the divisive question of federalism. The prospect is that there will be a long debate.

I turn to another part of the educational system - this one cited by Harvard's President, Derek C. Bok, in his just published annual report. It is as challenging as the first: he describes the American legal system as ''grossly inequitable and inefficient.'' He calls for fundamental changes in how lawyers practice and how they are trained. At one retrospective point he says that the public ''seems critical of all institutions and increasingly concerned that the country is no longer working well.'' This is sweeping enough. He says things are interconnected: ''International comparisons - in industrial productivity, infant mortality, the extent of pollution, crime, poverty, and many other social ills seem to give ample reason for this concern.''

A thoughtful congressman from Illinois, Democrat Paul Simon, points out that it is easier to write commission reports in Washington than to get something done. ''We are now in the buck-passing process,'' he notes. ''If the President is serious about this, he ought to reconvene the (education) commission and ask them to spell out what it will cost and who we pay for it. Without that, it is one more fine report that will gather dust.''

Here are some findings of the report:

* On international comparisons of high school students in industrialized nations for 19 areas of study, the US students were never first or second, and in seven areas were last.

* Average achievement of high school students on most standardized tests is lower than 26 years ago when Sputnik went up.

* The number and proportion of students showing superior achievement in college entrance exams have dramatically declined.

* Since 1969 science achievement test scores have steadily declined.

* Only eight states require high schools to offer foreign language instruction, an area the report cites as crucial.

* There is general decline in college admission requirements.

Among the commission's recommenda-tions:

* Teacher salaries must be increased.

* School days and school years should be longer.

* There must be more stress on basics, less on ''frill'' subjects.

* Foreign languages need greater emphasis at all levels and should be offered in elementary schools.

* Standards must be raised in all schools, elementary grades through college.