The Democrats have a new nightmare: they're afraid they may become the first party in history to score a complete political "gridlock."

Their convention is too big and Madison Square Gradens is too small. There will be less than two square feet for each of the 5,600 persons accredited to be on the convention floor. And when they start milling around then what?

Here is a convention official talking to network television producers:

"If you're going to try to have your people roaming around in the convention hall you better do it like Peter Pan. This convention floor may gridlock. Once you get on, you may not be able to get off."

Political conventions are always crowded. It's part of the beast. But seasoned convention planners who are doing their best to deal with an impossible situation, say this one will be especially chaotic.

"This convention will simply never be in order," said one official. "There are too many people."

Acutually, the Democrats would rather be someplace else. Atlanta, New Orleans and Chicago all have bigger convention halls. But each is in a state that hasn't ratified the Equal Rights Amendment. So the Democrats returned to the site of their 1976 convention.

"I think you'll see the floor literally lock itself. It almost happened in 1976 and we've got more peole now," said Elaine Kamarck, executive director of the Democratic Platform Committee."There's so much business this year everyone is going to stay in the hall. They won't be slipping out to dinner or to go shopping like they normally would do."

This may look like bedlam to television viewers. But it will have to be the way business is done for Democrats.

The configuration of Madison Square Garden is the same as in 1976. Main aisles are 10 feet wide. Side aisles are four feet wide or less.

But floor privileges this year have been given to 335 more delegates, 25 more security guards, 49 more television reporters, 60 more newspaper reporters and dozens more people in various other categories.Just last week 100 more floor passes were issued to supporters of Sen. Edward M. Kennedy (D-Mass).

Only about 60 percent of the people on the convention floor will be delegates -- 3,331 of them. Of the reaminder, 471 are televison reporters, 252 newspaper and magazine reporters, 150 pages and 100 ushers and security guards. In addition, every Democrat in Congress is given a floor pass. So is every Democratic govenor, lietenant governor, party state chairman and member of the Democratic National Committee. Special-interest groups representing teachers, women and labor unions also have floor privileges.

Kennedy and Carter forces have laid elaborate plans on how to marshal their forces on the floor. Kennedy delegates are being sold blue-and-white baseball hats with the words "Kennedy 80" on them.

But they can't hope to match the Carter presence. The president has more than 1,200 volunteers manning posts around the city. About 160 top White House aides, Cabinet officers and other top administration officials have flown in from Washington, causing some to joke, "Who's running the government this week?"

Carter's floor operation includes 350 whips. They've been issued 40 walkie talkies and 326 electronic beepers. The operation is headquartered in six trailers just off the floor

Cater has a "boiler room," a "situation room," a scheduling trailer, a "VIP" trailer, where campaign chairman Robert Strauss will entertain dignitaries, a press trailer and an arrangements trailer.

The nerve center will be the adjoining "boiler room" and situation room -- where former White House chief of staff and campaign manager Hamilton Jordan will preside over 14 aides assigned to monitor state delegations. They will have green phones connecting them with 14 counterparts -- called "cluster whips" on the floor.

The "cluster whips" are assigned to monitor state delegations according to their location on the floor. Each state, in turn, has from one to four state whips depending on the size of its delegation. Under the state whips are the deputy whips.

The Kennedy operaton is similar, but less elaborate. Carter forces who control the convention arrangements assigned Kennedy a workspace that trailers couldn't fit into. So they built a triangular structure that will serve as the Kennedy command center.