Mayor-elect Sharon Pratt Dixon's disputes with the outgoing Barry administration over policies and politics in the period between last week's elections and Mrs. Dixon's inauguration in January raise an old question: Why shouldn't Mrs. Dixon have been sworn in as mayor the day after the election?

Democracies all over the world change national governments the day after elections. There is no reason to delay the will of the people.

Moreover, the voters can make a more informed choice if the candidates are forced to detail their administrations, the names of their department heads, etc., before the election. Transition teams should be part of the candidates' platforms -- something for the voters to consider.

American state and local practice seems to be based on the long delay between federal elections and entry into office. That in turn was evidently caused by the poor condition of American roads in the 18th century. While the constitutional problems of changing federal practice are immense, there are no constitutional or practical difficulties in bringing a small city like Washington into the modern political world. We might even be a positive example for the rest of the country.

Mrs. Dixon should have become the mayor of Washington on Nov. 7. RICHARD J. HIGGINS Washington