IIt was said of Al Jolson, son of a cantor and trained to sing in the plaintive traditions of that craft, that he had a tear in his voice. It is in that spirit that I say there is something present in the voice of Ronald Reagan, too. It's a wink.

More and more, you get the feeling that the president is not totally on the level. He seems to say things that he can not fully mean, says them, maybe, because they are expected of him. They are what amount to verbal form letters that are signed "sincerely." You know better.

Take this little matter of whether his policies are "unfair" to the poor. Reagan says they are not while his critics say they are. In fact, at his last press conference, the president went out of his way to characterize as unfair that very characterization of him. He says he's nothing of the sort.

His supporters must have been disappointed to hear that. In fact, they probably did not believe it and, if a guess is allowed, they were not supposed to. After all, Reagan campaigned on the platform that he would be tough or harsh on the poor--what some could call unfair. That was the whole idea of reducing the welfare burden and eliminating legal services and cutting back on a host of social welfare programs. The poor were supposed to get hurt. It was, after all, supposed to be good for both them and the nation.

NNow the president seems to want it both ways. He wants both to be tough on the poor and not tough on the poor--or, to put it another way, tough and yet not considered tough. He wants his supporters to know that he's not been deterred from his program (the poor, of course, already know this) but he wants the rest of us to think somehow that he has.

In this and some other ways, Ronald Reagan is dribbling away his most valuable asset: his credibility. Regardless of your opinion of Reagan, you had to concede he did what he said he would do. Indeed, this was something Washington learned with dismay, even shock. And it was something in which Reagan supporters took enormous pride. Their man was not just another politician. He meant what he said and did what he promised.

Increasingly, that seems not to be the case. When it comes to budget deficits, for instance, what was termed an abomination during the campaign can now, somehow, be tolerated. And when it comes to his economic program taking hold, last spring became last fall and now, it turns out, the right date will be next summer when the tax cut takes effect. In other words, it begins only when things start to get better. Up to then, it's Jimmy Carter's old program that's at fault.

Similarly, the president promised that the recession would "bottom out" by the second quarter of this year. We are in that quarter, but like the economic program itself, the upturn is a mirage that always seems to be in the distance. The economic revival is now promised for the second half of the year.

Reagan is not merely playing with words. He is also playing with numbers. At his most recent press conference, he said Social Security was not "touched" when in fact it had been cut. He said programs for pregnant women had not been reduced, but merely merged with others. They were cut--by about $200 million. He said the overall poverty budget was increased. It wasn't. The new money went for defense. If the poverty budget had been increased, Reagan would have to concede failure. After all, he was not elected to do that.

These are not examples of the by-now-famous Reagan penchant for getting facts wrong and history all bollixed up--statements that send reporters to their reference books and White House spokesmen to the lectern to attempt clarification. Instead, these are attempts to have things both ways, to be responsible for successes and not for failures--to be the guy who somehow manages to reduce the federal welfare budget and yet not hurt the poor.

In this, Reagan is turning out to be no different than his Democratic predecessors, some of whom called for both fiscal restraint and additional federal programs. Back then, people who wanted the programs more than they wanted fiscal restraint understood you could not have both. But they knew their president and so they knew what to expect.

It's the same now. The real message as usual is not in the words. It's in the wink.