Not since 1912, perhaps not since 1860, have conditions been so propitious for the emergence of a formidable new political party.

Over the years, third parties have had limited appeal in the United States because they generally sprang from revolts in one of the major parties. But today there appears to be widespread, simultaneous disaffection among both Republicans and Democrats.

Moreover, in Rep. John Anderson there is a charismatic leader who would make an ideal third-party candidate, since he has already demonstrated his power to attract not only independents, but many dissident Republicans and Democrats as well. Although Anderson ran strongly in several of the early Republican primaries, it must be increasingly clear to him, as it is to others, that Ronald Reagan, backed by the hard core of the Old Guard, is on the way to locking up the GOP nomination.

Hence, it is not surprising that the Illinois congressman, who originally discouraged talk of his heading up a third party, seems to be having some second thoughts. It is not likely that he will commit himself before the next few primaries, but if Reagan keeps rolling toward victory, it's a good bet that Anderson will make a move well before the Republican convention in July.

His situation is similar to that of Theodore Roosevelt, who in 1912 competed against William Howard Taft, then the incumbent president, for the GOP nominaton. Although Roosevelt appealed strongly to the party moderates, the Old Guard dominated the national convention and chose Taft. That led to the famous walkout, the development of the Progressive Party, and the nomination of Teddy Roosevelt as the leader of the rebellious Bull Moosers.

It was a valiant effort, but handicapped by a late start (the Progressive convention was not held until August), and, further, the Democrats were united behind a forward-looking candidate -- Woodrow Wilson -- which made for few defections to the Progressive. Besides, the Socialists, headed by Eugene Debs, also were competing for the liberal vote, and got over 6 percent of it.

Even so, in the general election, Roosevelt ran well ahead of Taft. Wilson, however, with only 41.8 percent of the popular vote, got elected by winning a majority of the electoral vote.

It might well have been a different story if current conditions had prevailed. Today, the Democrats are sharply divided with Carter again touching bottom in the polls on performance. The Republicans are bent on nominating a candidate so seemingly weak that the titular leader of the party, Gerald Ford, openly predicts his defeat. Meanwhile, the Gallup polling organization reports a record increase of independents, accompanied by erosion of Republican and Democratic ranks.

Roger Masters, Dartmouth professor of government, finds that "once a generation, the American political landscape undergoes a fundamental change." Although both major parties have been relatively unchanged since Franklin Roosevelt's victory in 1932, Masters says, "a realignment of the voters may well occur in 1980." If so, he forecasts, "it could well put John Anderson in the White House."

When Anderson calls for a "new coalition," he is echoing the slogan that launched the Republican Party and, in 1860, enabled it to become the first and only new party to win the presidency. Lincoln's successful coalition included Abolitionists, Free Soilers, Independent Democrats, Conscience Whigs, Know-Nothings, Barnburners and Prohibitionists. Lincoln got only 39.8 percent of the popular vote, but it was enough for an electoral majority.

In weighing his chances as an independent candidate, Anderson might give an ear to Sen. Adlai Stevenson III, who is retiring this year, mostly out of frustration with two-party politics. In talking (favorably) about the creation of a new party, Stevenson said, "it might start just as the Republican Party started -- no party at all, just the gathering of the forces for true reform." He said he had no definite ideas on how such a party should be formed. "It might," he thought, "just be a candidate who would go off and invite people to follow him."

Anderson wouldn't even have to do much inviting. He would have an army of volunteers at his side in short order, and there would be a surprising lot of private money available to him as an independent. It would turn the election into a real thriller.