The future of President Reagan's embattled economic program now rests squarely in his own hands, in the view of experts both in and out of government.
''I am waiting,'' says a senior government official, ''for the President to do something dramatic to save his program before it is too late.'' That ''dramatic something,'' the official says, would have to be a major tax increase , big enough to convince Wall Street and Main Street that government deficits are not going to soar out of sight.
Such a tax boost would amount to a tacit admission that the supply-side theory underlying Reagan's program is flawed and unable to stem the spreading tide of budget red ink.
Supply-siders claim that huge income tax cuts in the long run will generate abundant tax revenues by encouraging people to work harder, save and invest more , and boost their productivity.
''There is,'' says a member of the Federal Reserve Board, ''no emperical evidence to support such a view.''
Instead, as many experts see it, the President is trying to do more with less -- granting $749 billion worth of tax cuts over five years while reducing government spending by much less.
That gap between income and outgo was, under the Reagan program, to be closed by a fresh tax revenue from a surging economy.
So far the reaction along Wall Street has been skepticism , nurtured by concern over towering budget deficits that may force the US Treasury to shoulder private borrowers aside in a scramble for capital.
Mistrust among money managers paralleled by a tight money policy, on the part of the Federal Reserve Board, has kept interest rates high.
This, in turn, contributed to the current recession, which -- in addition to throwing people out of work -- further reduces government tax revenues and swells government outlays.
A Department of Commerce forecast of 1982 capital spending, meanwhile, says that US businessmen plan to spend 0.5 percent less on plant and equipment than they did in 1981, despite new investment tax incentives. Capital spending last year grew by a modest 0.3 percent, after adjustment for inflation.
Most critcs agree that the roots of recession antedate Reagan's accession to office and that the President should not be tagged with responsibility for the economic downturn.
Nonetheless, he faces a de facto situation of rising deficits, which his current policies appear unable to reverse.
The President's official family of top advisers now is almost unanimous in urging that he increase taxes, to keep the 1983 and 1984 budget deficits below $ 100 billion a year.
''Given sensible advise,'' said a senior official, ''and if he takes it, the President still can have an economic program that is great for the country.''
He ticked off positive elements of the Reagan approach:
* The President is bringing runaway social programs slowly under control, with the aim of shrinking government's share of the national economy.
* He is updating and enlarging the defense establishment.
* Inflation and interest rates are inching down, although the major credit belongs to the recession, not to the Reagan program.
Because he insists on boosting military spending by 7 percent yearly in real terms, Reagan is forced to slash deeper into already-diminished social programs, in an effort to curb the deficit.
That alone will not do the trick, his top aides tell him, warning of a prospective $130 billion shortfall in fiscal 1983, unless the President jumps the supply-side ship and comes up with substantial new taxes.