PERHAPS A FEW people have not yet had the chance for a truly leisurely cover-to-cover reading of the 1980 Democratic Party platform, as amended and adopted at the New York convention. We'll try to help.

While they were undoubtedly the most disruptive and dramatic, Sen. Edward Kennedy's minority planks on the economy were neither the most significant nor the most historic. That distinction belongs to the minority plank on the Equal Rights Amendment, which the delegates adopted without opposition from either of the two presidential candidates, Sen. Kennedy or President Jimmy Carter.

The language of the amendment is quite straightforward: "The Democratic Pary shall withhold financial and technical assistance from candidates who do not support the ERA." That is all. A candid bargain -- you want to use Multnomah County Democratic Party while pages to look up addresses, then you had better be "right" on ERA. Just exactly what "right" means is not totally clear. Does a candidate who, for example, opposed congressional extension of the ratification period for ERA quality for "financial support and technical assistance"?

If such a candidate does not qualify, then an awful lot of Democrats are going to have to choose soon between honoring their party's platform or working for some of the party's most distinguished officeholders in reelection campaigns. Sen. Ernest Hollings, who as his state's governor was given major credit for the Kennedy-Johnson ticket's carrying South Carolina, voted against the extension. Sen. Dale Bumpers, who effectively retired the formidable and troublesome (for Democrats, especially) Orval Faubus from Arkansas politics in 1970, is up for reelection. If the extension vote is judged to be a litmus test, then Sen. Bumpers had better forget in a big hurry any plans he might have had about using either the postage meter or the coffee machine in any Democratic headquarters in or out of Arkansas. The same holds for Sen. Frank Church of Idaho, who also voted against extension, as did Rep. Bob Eckhardt of Houston, the only Texan to have been elected to head the liberal Democratic Study Group in the House.

Present Democratic Party rules require that the presidential nominee communicate to the convention, in writing, any personal misgivings about any platform planks. Here is what President Carter wrote of the ERA "loyalty oath": "I am proud of the ringing endorsement of the Equal Rights Amendment contained in the platform."

The Democrats, who have survived and occasionally prospered for a lot longer than most institutions, somehow managed to get along for years without this kind of loyalty oath. Too bad they changed course now.