A seven inaugural ball - or party, as this administration is calling them - has been added to the official calendar to accommodate an extra 5,000 people, inaugural committee officials announced yesterday.

The party, which will be held at the Pension Building, was added to meet the "overwhelming demand," for tickets, said committee cochairperson Bardyl Tirana.

He said the committee had received a "higher rate of acceptances" of invitations, and was also preparing for an influx of responses to an extra mailing of several thousand sent after the committee received "feedback" from people left off the original list of invitees to the parties.

The party will start at 8 p.m., instead of 9 p.m. as the others will, so that new President Jimmy Carter and members of his family can add it to their schedule. A well-known band will provide music, Tirana said, although arrangements have not been made final.

New invitees may take their invitations to the Commerce Department's Great Hall and purchase tickets, Tirana said. Other invitees who have not received their tickets in the mail by now also must go the Commerce Building to pick them up. Tickets cost $25 each. The Great Hall will be open from 9 a.m. to 9 p.m. through Thursday.

Meanwhile, preparations for inaugural week, which officially starts today, are under way.

At the National Visitor Center, where 8,000 are expected to dance tonight at a folk dance and another 15,000 are expected for an official inaugural party Thursday night, workmen put the finishing touches on a glass window closing off one end of the gallery.

The opposite end of the huge hall will be covered merely with the translucent plastic, which cuts down on the breeze but "does not act as an insulator," center assistant general manager John J. Cuthrie said. Given Washington's current cold wave, the prospect of 15,000 party-goers shivering instead of dancing has some officials worried.

Guthrie said there is steam heating system along the back wall of the gallery and a nearly completed "forced air system" in the rest of the vast room. Combined, the two systems could raise the temperature to as high as 64 degrees - in normal weather.

"We don't know how warm it can get in this cold," he said. One possibility for warming, he said, would be to fire a "salamander gun," which he described as a long flame that would warm the air. "We'd have to do it before the people got there, obviously," he said.

An added freeze-factor to the inaurgural party at the Visitor Center is that guests will be expected to check and pick up their coats outside, where gaily colored awnings have been put up for the purpose.

The city wil have its own inaugural parade Wednesday, officials said. It will include a motorcade with cars representing city services and will have a float made by District children welcoming Amy Carter here.

The parade will start at the Armory at noon and is to reach Lincoln Park about 2:30 p.m. for a half-hour ceremony on "the meaning of the Democratic process." Top D.C. officials will take part. The City Council and school bands are to be in the parade. It is unknown whether Amy will attend. She has been invited.

Architects of the solar-warmed reviewing stand for the presidential parade said three days of sunshine are needed to store energy for warming. There also is an emergency electrical system but neither setup is designed to do more than "take the chill off," they said.