THERE WAS A TIME when the congressional members of the parties played a much larger role in selecting the party's candidate for president.

The Constitution itself made no provision for political parties. Indeed, the Federalist papers explained the separation of powers among the three branches and between the two legislative chambers as a means of preventing the rise of "faction" and the threat to the public good posed by "the conflicts of rival parties."

But by the close of Washington's second term, the two-party system was well developed. Each party nominated its presidential candidate by a caucus of its congressional incumbents. Presidents and legislators of the same party worked closely together, and the president, with appropriate deference to congressional sensibilities, functioned as the de facto leader of his party in Congress. John Adams and Jefferson led so effectively that neither cast a single veto.

The Federalist Party's congressional caucus ended with the demise of the party after the sweeping Democratic-Republican victories in 1800 and 1804, but the Democratic- Republican caucus continued for another two decades. When this dominant party itself began to split up in 1824, William Crawford, the presidential nominee of the party's congressional caucus, finished a poor third in the general election to his fellow Democratic Republicans John Quincy Adams and Andrew Jackson, who both defied the decision of the caucus and ran with the endorsement of their state party conventions.

In 1828, there was no caucus, and each of the candidates ran by nomination of one or more of the state party conventions. By the time Andrew Jackson ran for his second term in 1832, his efforts to lead and circumvent the Congress had earned him the lasting hostility of his own party's legislators. Knowing he could not win in a congressional caucus, Jackson organized the first national political convention of the new Democratic Party, and he won both renomination and reelection.

Jackson, however, never succeeded in leading his party colleagues in Congress. Some of his successors did better, notably Lincoln in a time of great crisis. But the divergence between presidents and legislators of the same party resumed under Andrew Johnson.

With at best four exceptions (unless President Reagan can regain the remarkable momentum of his first year), this divergence has continued ever since. Two of those exceptions -- during Theodore Roosevelt's presidency and Lyndon Johnson's first three years -- occurred in "normal" times. The other two -- during the Wilson and Franklin Roosevelt administrations -- occurred in the crisis periods of two world wars and the Great Depression.