Washington — Some 900 Democratic politicians will gather late this week in Philadelphia for a mini-convention that party chairman Charles Manatt insists on calling a national party conference.
Mr. Manatt explains the latter term was adopted because there will be no delegates in attendance and no platforms adopted.
Instead, as political observers see it, the participants, selected without any grass-roots input, will use their get-together June 24-27 as an opportunity to:
1. Put six potential Democratic presidential candidates on parade - former Vice-President Walter F. Mondale and Sens.Edward M. Kennedy of Massachusetts, Ernest F. Hollings of South Dakota,Alan Cranston of California, Gary Hart of Colorado, and John Glenn of Ohio.
2. Provide a forum for challenging President Reagan, particularly on the way he is handling the economy.
Attending the gathering will be 374 members of the Democratic National Committee; 374 participants chosen by state party committees; and 100-plus elected officials including mayors, governors, and members of Congress.
Senator Cranston, talking to reporters over breakfast on Monday, June 21, says of the convention: ''There will be good fun, together with some serious business.''
The conference is producing issue papers which theoretically could become the Democratic alternative to the President's programs. But the leaders of the gathering - in order to avoid any sharp clashes over policy - are seeing to it that resolutions will be broad enough to still any potential dissent. Manatt-imposed rules will prevent any jarring policy debate from breaking out on the convention floor.
Thus, as political observers here see it, the final product of the conference is likely to be relatively general and bland.
Some major policy thrusts, already circulating among leading Democrats, will be echoed in Philadelphia:
* A resolution endorsing a freeze on Soviet and US nuclear weapons arsenals. Here again the final paper will be broad enough to satisfy those who want an immediate freeze and those who seek a freeze with qualifications such as verification and a US arms buildup prior to the freeze.
* A resolution challenging Reaganomics. Instead of providing a specific alternative, the final resolution will likely be a broad one calling for lower interest rates, increases in productivity, more jobs, and a hold on inflation.
Thus this Democratic conclave, unlike its predecessors in off-election years, may well turn out to be more form than substance.
Democratic leaders want to give the impression that Democratic politicians of varying points of view came together, talked, and amicably agreed to resolutions on the major issues of the day. But more than anything else, they want to avoid airing sharp differences among Democrats on explosive subjects such as abortion, busing, prayer in the schools, and gay rights.