Boston — For liberal economists like Samuel Bowles and Jeff Faux, the presidential election campaign is proving to be an awful climax to a bad four years. They listen in surprise as Democratic candidate Walter Mondale promises a tax increase to reduce the deficit while Republican President Ronald Reagan says he will raise taxes only as a last resort.
These positions on the deficit are not only contrary to tradition; after all, it has usually been conservatives who fuss about deficits, not liberals. But also tax boosts, in the view of such Keynesian-inclined economists as Mr. Bowles and Mr. Faux, are dubious economics.
Many economists, as Bowles explains, are concerned over the possibility that a recession will hit the economy sometime next year. By then the recovery will have lasted the average life span for postwar expansions. So he worries that a tax hike could worsen any recession. It would take money out of the hands of consumers.
''His (Mondale's) understanding of economics is very different from mine ... if he thinks he can put Americans back to work by balancing the budget under present circumstances,'' Bowles said. ''(If) you withdraw that stimulus from the economy under current circumstances, you would drive the unemployment rate into the high teens or the 20 percent range.''
Mr. Bowles, an economist at the University of Massachusetts in Amherst, and Mr. Faux, director of the Project on Industrial Policy and Democracy in Washington, aired other laments about the state of liberal economics in an interview here. For instance:
* Mondale and most of his Democratic rivals for the 1984 nomination agreed on the need for increasing military spending. They also spoke about some sort of belt-tightening by consumers and government to permit more private investment. They even held that business profits were a basic guide to the economy.
By earlier postwar standards, those are all rather ''un-liberal'' positions.
* Many ''liberal'' economists are no longer so liberal. For instance, Charles L. Schultze, chairman of former President Carter's Council of Economic Advisers and now with the Brookings Institution, has spoken out against industrial policy; that is, the guidance of private investment by government, usually in cooperation with industry and labor. Both Faux and Bowles advocate industrial policy.
Some ''liberal'' economists have also decided that the only way to trim the deficit now is to go after middle-class entitlements, such as medicare and social security, Faux complains.
''To some extent they are politically eating their own,'' he says.
Faux maintains that liberal Keynesian principles - such as the idea that deficits stimulate a recovery - have been confirmed by the behavior of the economy over the last two or three years.
Yet many liberal economists, ''for whatever reasons, whether it's failure of nerve or a turn to more conservative politics or whatever, have not had the courage of their own convictions.''
* Conservative economics has received enormous financial support in the last 15 years. Such organizations as the American Enterprise Institute and the Heritage Foundation have spent millions on what Bowles calls ''right wing'' economic research. Liberal economics has not enjoyed such generous backing. And even the so-called liberal Brookings Institution in Washington has proved less liberal, sometimes even conservative.
Bowles spoke of how the liberals' spectrum of economics was ''essentially silent or quiet'' in the late 1970s and early '80s and of the ''really extraordinary pace of the ascendancy of conservative economics.''
The fundamental problem for the liberals, he maintains, is that they had difficulty explaining what went wrong with the United States economy in the 1970 s - the slowdown in productivity and output, and weak profits. Their explanations, such as flatly blaming the 1973-74 quadrupling of oil prices, were ''superficial,'' since the trouble had started before then.
Another problem for liberal economists was their ''one-line prescription'' of a redistribution of income from the rich to the middle and poor that would support higher levels of demand, and therefore higher levels of profits. ''A lot of people came to suspect that that wasn't true,'' said Bowles.
Many in the economics profession came in the 1970s to accept the thesis that there was a necessary trade-off between business investment and consumer spending. This ''knocked out the props'' from under the liberal economists' view that growth could accommodate both at the same time.
Bowles maintains that liberal economists have been wrong to give up the argument that you can increase significantly both investment and consumption in a slack economy.
''We can produce more of everything,'' he said. ''We are not operating under capacity constraints.''
Bowles also holds that ''egalitarian social policy'' remains good for the economy, just as it was when liberals developed their ideas in the 1930s, '40s, and '50s. He does admit, however, that liberals have learned something about the need to look after the supply side of the economy, vs. the demand side. He sees, among other things, a need to weaken the adversarial stance between labor and management.
Faux argues that Presidents Carter and Reagan, rather than attempting to remove inflation from the economy through a recession, should have employed an ''incomes policy'' (usually wage and price controls) to keep costs and prices from rising so fast. The direct attack on inflation, he says, would have permitted the nation to continue the ''liberal vision.''
Instead, Charles Schultze and other economists who ''used to be called liberal essentially ... are saying, 'Well, Reagan is more or less on the right track,' '' said Faux.
''The result is that in the mainstream debate there really is ... nothing left of what the liberal position used to be.''
Faux and Bowles have been trying to restore true liberalism, as they see it. Both have written recent books. Faux is co-author of ''Rebuilding America'' (Pantheon) and Bowles co-author of ''Beyond the Wasteland'' (Doubleday). They have been writing op-ed pieces and talking to the press. But it is proving an uphill battle. The Mondale election campaign shows this, with the Democratic candidate moving toward the economic center to capture middle-ground voters.
''There is no real debate,'' complained Faux.