The nation's Republicans are working against the clock to answer two key questions: Can conservative Ronald Reagan possibly attract enough independent and Democratic votes to win in November?

An if he is likely to lose, has former President Gerald Ford time enough to challenge him for the GOP nomination?

The consensus among political experts is that time has probably already run out for Gerald Ford, though he still appears the stronger choice to beat Jimmy Carter in November.

But some experts caution: Don't count Ronald Reagan out as a national candidate for the fall. He is not, they say, "a McGovern or a Goldwater" -- fringe candidates who led their parties to one-sided defeats in 1972 and 1964. Intellectuals don't want to take him seriously, but he does well with working-class voters. He would take the West, challenge President Carter in the South, and do well in the pivotal Midwest states like Ohio and Illinois, whose southern regions titled toward Carter in 1976, they say.

"Winability has long been used as an argument against Reagan, and has been proved wrong," says California pollster Mervin D. Field."in 1966, after he became the darling of the conservatives for his fund-raising pitch for [Sen. Barry] Goldwater, people thought Reagan would have been easier for Pat [Edmund G.] Brown to defeat for the governorship than the moderate, dynamic George Christopher, mayor of San Francisco. Brown was hoping his opponent would be Reagan. But it blew up in his face. Reagan beat Brown.

"The unpopularity, the negative quotient-of Governor Brown was the most critical factor in his loss," Mr. Field says.

The November 1980 election similarly could come down to a test between negative ratings, he says.

"Reagan's age, the feeling 'he's out of it,'" could be offset by "disappointment with Carter on inflation and foreign affairs," Mr. Field says. "In the Truman-Dewey, Nixon-Kennedy, Johnson-Goldwater elections, the winning candidate was the one with the lowest negative score, not true majority public support."

"Reagan is the opponent of choice for Carter," says I. A. Lewis, director of the Los Angeles Times Poll, a point on which most analysts agree. "But Reagan can reach across and cause mischief in the Democratic constituency," Mr. Lewis says. "Reagan appeals to blue collar, working-class voters. He can win Democratic votes."

"Carter could beat Reagan more easily than he could Bush or Baker," Mr. Lewis says. "A moderate Republican would appeal to moderate Democrats, while upper-income Republicans might defect from Reagan to the Demcorats. Ford is of course, the strogest in the polls against Carter. But if he became a candidate, he could sink the same way Kennedy did after he declared."

Elections analyst Richard Scammon, who thinks a candidate must command the political center to win the presidency, gives neither Reagan nor Ford much chance.

"The general opinion -- that Ford is too late -- is correct," Mr. Scammon says. "A Ford candidacy wouldn't have much meaning unless he persuaded the other moderates to withdraw, which they apparently won't do."

In terms of a national election, Mr. Reagan's New Hampshire victory last week is less imrpessive, Mr. Scammon says. "Reagan got 48 percent in New Hampshire against Ford in 1976, and 49 percent in 1980 with a superfluity of anti-Reagan candidates.

"The odds are very good that Reagan will not be successful in November. It looks like the Republicans have done it again. Down-the-line conservatism has triumphed over down-the-line center forces."

Austin Ranney, American Enterprises Institute authority on the US election system, sees only difficult scenarios ahead for a late Ford entry into the race. First, if Mr. Reagan takes perhaps 40 percent of the delegates to the convention , then "theoretically there could be a brokered convention with Bush and [Sen. Howard H.] Baker throwing support to Ford."

"But as we've already seen," he says, "much of the eroded Bush support has gone to Reagan, not Baker." Neither party has power brokers any more, he says: "The candidates are organized like entrepreneurs, to win for themselves, not to deliver to someone else."

"Given the triumph of populism in politics today, the notion a candidate can enter late and take the nomination away from a candidate like Reagan, in it from the beginning, must be questioned," Mr. Ranney says.

"Fordhs best chance is to enter all the remaining primaries he can, do well, beat Reagan in a couple of head-to-head contests, outshine Bush and Baker. He would claim that if he had entered early, he would be the front-runner and not Reagan.

"The longer Ford waits the more difficult his chances. Bush has clearly said he won't get out if Ford gets in. Bush will likely split the moderate vote with Ford."

Primary deadlines are fast closing for Mr. Ford. Secretaries of state in many remaining primary states can still put his name on the ballot, even though candidate filing deadlines have passed. But even for that route, March holds all the time he has. His political home state Michigan ballot will be set March 21, California's March 31.

Another Ford option, according to Mr. Field: Skip the primaries but go on a national speakign tour, attacking President Carter, saying "I want to offer a choice," and hope the other candidates are viable enough to prevent a Reagan first ballot win at the July Republican convention in Detroit.