When Democrats gather

As Democrats gather in Philadelphia today they have an opportunity to act on the recent warning of their national party chairman, Charles Manatt:

''The pitfall is an overreliance on the negative perception of Reagan's policies. Sooner or later we will be hurt if we do not come on strongly enough with a positive message.''

Such a message could emerge from the workshops at this midterm conference, which party officials are trying to distinguish from the ''mini-conventions'' of previous years. Unlike those post-election confabs, this pre-election one could have an effect on the fall congressional campaigns. Certainly there is room for creative forging of positions on the seven workshop topics: foreign policy, defense, and arms control; economic growth; human capital; individual rights and personal security; food and agriculture; environment and energy; making government work.

However, draft positions for discussion are reportedly generalized, no doubt in an effort to avoid disunity. And the media focus is tempted toward the parade of 1984 presidential hopefuls who will be wooing the party faithful with speeches and hospitality.

Personality is part of politics, of course. But these candidates as well as the other thousand participants can start serving the public, not to mention their party, right away by offering definite alternatives to debate against Republican policies.

They could, for example, spell out ways to implement what is said to be the conference draft statement's main addition to 1980 echoes: a strong endorsement of a mutual and verifiable nuclear freeze. They could address rather than simply deny arguments that a freeze would place the United States at a disadvantage despite the enormous nuclear arsenals on both sides.

On many matters the individual candidates or other voices have already been sounding something besides echoes. To consider only Topic A, the economy: one suggestion is as specific as eliminating or reducing the tax on savings. Another is a broad recognition of the need for new economic approaches in light of the change in the workforce to a majority in service, high-tech, and information sectors rather than the industrial and agricultural sectors.

There is the idea of a progressive and personal expenditure tax; a phased-in rise in gasoline taxes, with automatic relief for low-income groups, in order to ensure against future energy crises. There is the flat-rate tax without deductions or at least the reduction of tax breaks to increase government revenue without general tax rises. To keep a handle on inflation there is a suggestion for wage-price guidelines supported by tax incentives or penalties. There is the proposal for a new federal Reconstruction Finance Corporation and/or state-level development centers to promote new businesses through seed money and expert information.

These are not necessarily ideas to be settled on. But a range of possibilities has to be considered if the Democrats are to help provide the viable economy to back their conference theme of ''Fairness to All.'' Not only traditional Democratic concern for the disadvantaged but concern for efficiently supplying the means - this must be part of the ''positive message'' the national chairman calls for.