Carl D. Ford, a Laurel, Miss., lawyer and conservative Democrat, sat down the other day and wrote a letter to President Reagan, the man he helped put in the White House in 1980.

"From your action to date," he wrote, "I cannot tell if the anger you have expressed (at the Korean airliner incident) . . . is over the actions of the Russians or having your vacation cut short. . . . As miserably as he handled the Iranian hostage situation, even Jimmy Carter didn't publicly give his leisure time priority. . . .

"Don't be too smug in thinking that the conservatives have no place to go in 1984. I assure you that if you show no more respect for Larry McDonald (the Georgia congressman who was among the 269 victims) and for this difficult situation than to go through a charade at the U.N. and . . . resume business as usual-- grain deals, pipeline and other technology transfers--then you have convinced me that a vacation is more important than standing on principles. In that event, I intend to exercise an old and honorable southern Democratic tradition on Election Day 1984, and go fishing."

When I called Ford and asked his permission to reprint part of his letter, he not only agreed but said he would be happy for everyone to know he thinks the president he strongly supported until Labor Day "is acting like a wimp."

Paul Weyrich, head of the Committee for the Survival of a Free Congress, received a copy of the Ford letter-- and, he says, "an incredible number" like it-- after writing a column in USA Today expressing his own criticism of Reagan's "mild" reaction to the attack.

Weyrich says he is convinced that, more than any action of his presidency, the Reagan decision not to retaliate with strong sanctions against the Soviet Union may cost him "the militancy of his militant supporters," if not their votes, next year.

Howard Phillips, chairman of the Conservative Caucus, another New Right group, made the same point with a vivid analogy. "This was Ronald Reagan's Falkland crisis," he says, "and he did not respond appropriately."

The criticism of Reagan's "moderation" has been a constant theme of such New Right leaders as Weyrich, Phillips and Conservative Digest publisher Richard Viguerie. The White House has tended to brush off this right-wing attack on the grounds that, come Election Day, "these people have no place to go."

That is still the attitude. One Republican strategist with very close White House ties accused the three critics of "playing to their mailing lists," and pointed out that support of the president's response has been nearly unanimous in Congress. Other Reagan advisers argue that by being strong in his rhetoric but measured in his actions, Reagan probably has assuaged fears that he was "trigger- happy" and thereby strengthened his position with the general public.

But as one who has endorsed the president's actions in this case and has dismissed the threat of political retaliation from the New Right in the past, I am beginning to think the White House may be a bit quick in assuming there is no political risk in antagonizing that faction this time.

Carl Ford and the others who have been telling the pollsters (by a 52-37 percent majority in a Gallup Poll for Newsweek, for example) that Reagan's response was "not tough enough" are not all fanatics.

Anti-communism is a bedrock issue for the conservative movement. Reagan almost beat Jerry Ford for the nomination in 1976 by inveighing against "d,etente." The idea that their president is less tough than Margaret Thatcher, let alone Jimmy Carter, is a shattering one for those who have followed Reagan-- and particularly for the shock troops of his political army.

Viguerie is right when he says that in the last two closely fought elections the Republicans lost--with Richard Nixon in 1960 and Ford in 1976--one of the factors contributing to defeat was the fact that "conservatives were upset and we didn't knock ourselves out working."

I remember Lydia Miller, a Reagan delegate from Missouri at the 1976 Republican convention, telling me when Ford won that working for him that fall could "no way" be like the "holy crusade" she had mounted for Reagan. "I'll support the whole Republican ticket," she said, "and we will do the routine, mechanical work of the campaign. But there's no way it can be the same."

That disaffection hurt Ford in 1976, and a similar degree of disillusionment in the heart of his support could be a terribly serious problem for Reagan for 1984, if it persists. Maybe he can rekindle the fires. But the loss of enthusiasm and the threat of a less than all- out effort from the hard-core conservatives is a real loss politically--one that cannot be easily dismissed.