On Saturday, President Bush completes his first 100 days in the White House - the point at which new chief executives traditionally start receiving their first report cards on their presidency.

Even before that artificial milestone was passed, the grades started coming in. Generally, they are lower than Bush deserves.Why? Because the marks are based on the false assumption that a fast start is always best. But jack rabbits may win sprints but not marathons. Besides, fast starts with plenty of changes are anything but best if one believes with the Founding Fathers that the best government is the least government.

What did the critics really expect? Sharp shifts in course from a man who helped Ronald Reagan steer the ship of state for the past eight years? Get serious.

Americans did not vote for change last November. If they had, Michael Dukakis would be in the White House rather than remaining in the governor's office in Massachusetts.

The broad rule is that the worse shape the country is in when a new president takes over, the sharper and faster are the changes he makes. But Bush inherited a country at peace and riding a wave of economic growth that has lasted an unprecedented seven years, with unemployment at a 15-year low.

Moreover, whereas Reagan's style in dealing with Congress was confrontational, Bush's is conciliatory. But then Bush doesn't have much choice. Whereas his fellow Republicans controlled the Senate during much of Reagan's administration, Democrats now control both houses of Congress.

Faced with these circumstances, Bush has:

- Acted quickly to propose a plan to deal with failing savings and loan institutions. Congressional committees have made significant changes in it.

- Negotiated with Congress a new $28 billion deficit-reduction plan that keeps Bush's campaign promise of no new taxes but leaves for the future the hard choices about eliminating red ink.

- Submitted a $441 million education package that has met with little enthusiasm from Capitol Hill.

- Secured an agreement from Congress to continue non-military aid to the Contra rebels in Nicaragua but halt the aid in November unless four congressional committees let it continue.

- Submitted proposals to improve ethics in the federal government.

- Moved to use the full resources of the government to deal with the Alaskan oil spill, after having initially underestimated its seriousness.

- On foreign policy, Bush has yet to fully define his approach to East-West relations in view of the changes in Moscow. But what's the rush when present policies have helped prod Soviet leader Mikhail Gorbachev to make more and more concessions?

Though the critics insist that this record justifies the claim that the new administration is drifting, the stock market evidently isn't bothered by Bush's gradual approach to problem-solving. The Dow Jones Industrial Average, which stood at 2,235.36 when Bush took office, has in recent days risen above 2,400, a post-crash high. That's certainly an encouraging vote of confidence.

Besides, the initial report card now being given the Bush administration is the one that matters least. The ultimate tests of presidents are events that follow no timetables. George Bush has not yet faced a major crisis. When he does, the public won't need professional pundits to tell it the kind of grades the 41st president deserves.