Among the myraid choices confronting President-elect Ronald Reagan are two that will tell whether his administration follows pedestrian Republican predecessors or sets a radical new course for the nation.

Choice No. 1: Will Reagan follow widespread advice and dump two of his campaign's national security advisers, Richard Allen and William van Cleave?

Choice No. 2: will he pick a prestigious Wall Street favorite with high governmental experience as secretary of the Treasury or risk the establishment's scorn with an unknown but brilliant iconoclast named Lewis Lehrman?

The choices are important both in themselves and for symbolic content. Purging Allen and van Cleave, advocates of true defense preparedness and toughened foreign policy, could be a move back toward the very detentist policies that have weakened that nation. Avoiding the establishment's displeasure in filling the Treasury post would signal the embrace of economic orthodoxy.

Taken together, those two steps would signify Reagan's intention to replicate the Nixon-Ford administration: eight years of declining world prestige and a deteriorating economy, accompanied by the Republican Party's stagnation. They have acquired a sheen only in contrast to the four Carter years that followed.

Indeed, widely speculated choices for senior Cabinet posts are all Nixon-Ford retreads. So are many of the advisers in place for the transition. In addition to their advantages of numbers and proximity, these Nixon-Ford veterans wear the cloak of respectability. Their appointment will earn instant approval from commentators who never wanted Reagan for president anyway.

The transmutation of Ronald Reagan as Gerald Ford's political executor might have been unavoidable had he won narrowly, as expected. Some far-sighted supporters now tell him that his landslide carries a mandate that not only permits but requires him to build an administration with new and distinct policies, however unfamiliar and radical to establishment eyes.

The fate of Dick Allen, Reagan's Washington consultant on foreign policy the past four years, is a test case. Some Reagan advisers have copied the Queen of Hearts, who in ordering off Alice's head insisted: "Sentence first -- verdict afterwards." Before conflict-of-interest charges against him could even be studied, these advisers were spreading the word that he was gone from the future administration (even if retained to help plan the transition).

There is no evidence of complicity by Henry Kissinger (who telephoned Allen condolences about his troubles). But Allen is viewed by conservative Republican politicians as a safeguard against the return of Kissinger or Kissinger-style detentism. In urging Allen to fight his detractors, one such politician wrote him: "You cannot lose this battle, for it is at the heart of the fight for the mind and soul of the Reagan administration's foreign and defense policies."

Van Cleave, Reagan's principal adviser on arms control, has no ethical charges against him. But when the Reagan campaign Oct. 29 repudiated his public statement that the Reagan administration might have to increase defense spending more than 7 percent a year, there were echoes of President Ford's sacking of James Schlesinger as defense secretary for refusing to cut defense spending. Like Allen, van Cleave has been privately read out of the new administration by some Reagan insiders.

As for the key Treasury post, publicly mentioned possibilities are, to the man, Nixon-Ford alumni: William Simon, Alan Greenspan, Charls Walker. All are publicly committed, as is Reagan, to sustained tax reduction. But since none of them supported that policy in their Nixon-Ford incarnations, the question arises: would they opt for caution and respectability in a Reagan administration?

That question cannot be asked about Lew Lehrman, a 42-year-old Yale- and Harvard-educated self-made millionaire from New York City and an innovative economic theorist. At the Treasury, Lehrman would insist on supply-side theories with radical tax reduction. He would start reviving the dollar by moving toward a return to gold backing. He is no favorite of Wall Street but has fervent support from the supply-side economic clique and a wide Republican spectrum in Congress ranging from moderate Rep. David Stockman of Michigan to conservative Sen. Jesse Helms of North Carolina.

They and other Republican politicians want to see senior Cabinet members whose names are not household words. That would take political courage for Reagan. So would appointment as secretary of state of a name that is familiar: Democratic Sen. Henry M. Jackson. Some of Reagan's Nixon-Ford advisers (especially Bill Simon) bitterly oppose Jackson, but he would be a departure from the unhappy Republican past and an opening to coalition politics.

The last three presidents to begin new administrations -- John Kennedy, Richard Nixon and Jimmy Carter -- were shackled by hairline victories. Not so Reagan, who faces unlimited possibilities with no need to embrace names and policies of a past more associated with failure than success.