SELDOM HAS there been a Fourth of July marking such a marvelous leap forward of the values on which the United States was founded. Just in the past year, a major region of Europe has been freed and allowed to resume working out a destiny of liberty; the Soviet Union has experienced democratic stirrings of dimensions unseen in Russian history, and the Third World has moved erratically but hopefully toward seating the principles of representative government and economic choice. No less a light than Nelson Mandela has just bowed to the American Declaration of Independence for summoning South Africans ''to join in the struggle to guarantee the people's life, liberty, and the pursuit of happiness.''

The United States, of course, did not itself invent democracy and free enterprise. These were the products of many minds and many hands. But this country can take pride in having assembled these elements and put them into effect with its own energy and spirit. It did so with a characteristic claim that these values were not only practical and elevating for Americans but equally worthy and useful for others. Then and later, many were to doubt on both pragmatic and philosophical grounds the universal validity of the American creed, or they were to question the specific fashions in which it was elaborated. But if American policies were not always designed and conducted wisely -- and certainly this is so -- then the American model nonetheless has often shone brightly and has exerted a powerful influence on other peoples reaching to make their own society more just.

What might Americans conclude about the manner in which recent history has seemed to certify the American dream? There is reason to share in the excitement of a citizen's participation in a great cause. But it is early and vain to imagine that history flows without interruption and in only one direction. It is even more foolhardy to take others' turn to the American idea as occasion to slacken the effort to make that idea flourish more generously and fairly here. The premise on which this country was founded was not that a particular system ensured a particular political or social result. It was that the American system offered citizens of the republic the best conditions in which they could labor for their own ends, individual and collective. The rest of it was always up to them, and it still is.