Sixteen whiffy-city blocks up from the klieg-light razzmatazz outside Madison Square Garden, one of the largest, most tightly-knit single-issue, delegations in town was reveling in total victory, packing up and pulling out for good before the Democratic Convention even opened. For these 80-odd traveling Baltimore Orioles fans -- whose dream tickets are for Section 34 back home in the stadium -- the trip had been worth every minute.

But for the individual Democratic delegate in and around the Garden at midweek, gauging political cause and effect is not nearly so simple. When energies and emotions are sapped on opening night in a battle over a party rule, and when the next day's fight card is filled with editing contests for a mini-bookful of hodge-podge platform planks, what will a delegate be able to point to with great pride next week and still hold an audience?

No, this won't be the old why-bother-to-have-a-convention argument; even if the sole mission of such a gathering were merely to ratify primary results, there would be therapeutic and valuable reasons for bringing together some sampling of party faithful from around the country -- the reward, the outing, the magnet and showcase for all those extraparty movements, demonstrators and assorted glommers-on.

It isn't that the Big Rules Fight was a nothing, either, after all, that one settled the nomination question -- for those who thought there still was one -- and almost emptied the house for the keynote speech and the afternoon agenda yesterday. That work -- on platform -- is what has turned out to be the needlework for any delegates with nothing better to do.

Aside from the prime-time platform battles that have served to point up and redefine differences between President Carter and Sen. Kennedy, the platform might as well be an overstuffed pasteup of leaflets from the vent-a-cause parade that marched through the city three days ago.

Heaven help the delegates if there's a quiz on the platform tomorrow -- testing understanding of the proposals on the handicapped, Martin Luther King Jr., domestic violence, American Indians, Americans living abroad, taxes on married working couples, "excessive or illegal police force" or what to do about biomass, fusion and geopressure.

And if your run-of-the-Garden-variety delegate hasn't a clue, what conceivable difference will it make to anybody beyond the 12-mile limit? At least for better or worse, even casual followers of last month's Republican doings in Detroit may have some general perception of, or opinion on, the philosophies behind the GOP platform.

Platform planks aren't known for their shelf-lives, but over the years the collective thinking that goes into a party's assessment of the issues has reflected -- and even directed -- national policy. The wrestling of Democrats over civil rights, free silver, Vietnam or Prohibition surely had such effects.

Without this sort of thrust in the 1980 platform, the definition of party direction -- or what's in it for the voter -- is left to President Carter to shape in the next 12 weeks -- and therein lies a vacuum not unlike the uneasy atmosphere that prevailed in the hall here yesterday afternoon.