Only a handful of people in a basement room below city hall know much about it, but according to information slipped to me in a plain manila envelope by an always reliable source named Delores, an attempt will be made to stage several political party primaries in this city any day now -- probably today.

Don't look for posters on trees, candidates on the tube or red, white and blue bunting on the rostrum at your community center -- for this is a slick operation, run under a cover of a gambling referendum that is to be held at the same time in the same places around town. The objective is to settle a number of sensitive and possibly even important political decisions without too many voters getting in the way. And if a few people do discover the scheme and try to participate, an elaborate series of procedures has been devised to confuse and embarrass the most worldly League of Women Voters veteran.

Still, because there are some residents who may care enough to send the very best to the national political conventions this summer, here are some ways to crack the code and reasons for having your opinions recorded:

Those residents who think they are on a roster of 253,628 people registered to vote one way or another in the District are divided into groups with different options. The largest of these has the names of 199,361 people signed up to vote in the Democratic Party primary -- for a presidential candidate, convention delegates and national and local party offices.

These voters will be handed a fistful of ballots that will need special sorting. First clue: three of these ballot cards will be marked "A" --one for Edward M. Kennedy and delegates and a third for Lyndon H. LaRouche Jr. and delegates.Each voter may pick one of these cards to punch out; the unused ones should be put in an envelope to be filed separately.

There's more to the A-card game, though some of these other contests are fairly cut and dried. The convention-delegate candidates are divided by sex, and a voter may choose no more than six or seven (depending on what the ballot says) from each sex. Then on the flip side of this card is a contest between Del. Walter Fauntroy and his trusty opponent, "Write-In If Any"; and there are other unopposed candidates for national committee offices.

Now to a "B" ballot, on which voters may select up to 12 of 14 people running for atlarge seats on the local party committee. On the other side of this card are candidates for ward seats on the committee.

There is a "C" ballot, too -- the gambling question.

Some of the liveliest battling has been among the local Republicans -- a small but divided number with sharply divergent views of what the party should be about in the District, as well as who the presidential nominee should be. This balloting is confusing, too, starting with an "A" card for president. Ronald Reagan isn't on it. But John Anderson, now an independent without an official primary to run in, and Philip Crane, who has withdrawn from the Republican race, are. So are George Bush, Benjamin Fernandez and Harold Stassen.

For U.S. House delegate, GOP voters can write in anyone because no one is listed. Then on both sides of a "B" card are convention-delegate candidates who are uncommitted or committed to Anderson or Bush. A voter may pick no more than 14. Alternates are listed on a "C" card. "D" is the GOP gambling ballot.

The roughest competition is for control of the party, which pits two huge slates against each other on a paper ballot that is more than a foot and a half long. The regular D.C. Republican Committee Slate -- including Chairman Paul Hays and D.C. Council member Jerry A. Moore Jr. -- is being challeged by a slate of older-line party members favoring a "Proposition 13" and Ronald Reagan. The regular, or "Blue Ribbon," committee slate lists 38 white canidates, 30 blacks, one Oriental and one Hispanic member, while a breakdown of the other slate shows 62 whites, four blacks and one Oriental. The regular team has registered 2,700 new GOP voters since February and generally supports efforts to win ratification of the D.C voting rights amendment.

Statehood Party members -- there are 1,513 registered -- may write in a candidate for delegate to the House and may vote on gambling. Anyone else, independents or members of other parties, will receive only the gambling ballot.

Gambling or not, even Jimmy the Greed isn't sure what odds to give on when the D.C Board of Elections and Ethics might finish counting everything. The board's chairman, James Denson, may know something, though-he was last seen preparing to leave town for Paris on that free VIP flight provided by TWA.