They started out at 7:30 yesterday morning in grim-faced picket lines in front of the Kennedy Center and ended up at 20 past midnight dancing in the parking lot.

The strike which the Instant Charge workers at the Kennedy Center had begun, garnering support of employes who belonged to affiliated locals, ended a little past midnight when negotiators reached an apparent settlement after eight hours of negotiation.

Although there seemed to be some disagreement over the terms of the settlement, it was enough to send back the 30 or so stagehands who had stayed out of work yesterday to honor the picket line.

The solution also averts the possible embarrassment of the Cuban National Ballet, set to begin performances tonight, which would otherwise have faced the sticky problem of whether or not to cross the picket line. The State Department had cautiously pointed this out to both the International Alliance of Theatrical Stage Employes and to the Kennedy Center's executive director, Martin Feinstein.

Before the fatigued negotiators went home last night, clusters of union members who stayed out of work but not home, lent their support by simply showing up at the Kennedy Center and watching the picketers.

Box-office Staff did not report for work, and members of the Kennedy Center Orchestra did not go to their scheduled 10 a.m. rehearsal. Many of them congregated along the concrete planters in front of the Watergate or lounged on the grass of the side of the Center. Musicians piled their assortment of cellos, violins and horns on the sidewalk beside them.

In addition, two members of the National Symphony Orchestra, now on vacation, joined the picket line.

"We're supporting their strike because they supported ours," said clarinet player Loren Kitt, smiling as he walked in a circle of picketers outside the Hall of States at the Center. The National Symphony members struck last fall.

But despite the scene outside the Kennedy Center, last night's performance of "Home and and Beauty" at the Eisenhower Theater "went off splendidly," according to Kennedy Center spokesman Leo Sullivan. The substitute staff celebrated their accomplishment with champagne.

When Teamster truck drivers arrived in four 45-foot vans earlier in the day - carrying equipment and costumes belonging to the Cuban National Ballet, scheduled to begin performances tonight - they would not unload their trucks. The four drivers sat around the loading dock playing gin rummy, waiting for some resolution.

The Center was hit hardest by the loss of about 30 stagehands who had been expected to show up yesterday at 8 a.m. to set up props and other material for the Cuban National Ballet.

The Ballet's Cuban technical crew stood patiently with the other employes outside. "We just have to wait to see what happens," said technical director Salvador Fernandez.

"For the Cubans to cross the picketline, well, visually," said the show's American production supervisors, Gilbert Hemsley, "well, it would just have to be well thought out."

The local support for the Instant Charge workers took Kennedy Center management by surprise, since the strike was not officially sanctioned by the International Alliance's president, Walter Diehl.

The Kennedy center is not planning to take action against the striking Instant Charge workers - whose job technically are in jeopardy because the strike has not been sanctioned by the International's president. Martin Feinstein, executive director of the Center, said yesterday that "there's one thing I've learned in business. Recrimination does not pay."

Feinstein said that the Center had been prepared to have the Ballet begin scheduled performances tonight. "We would use our own administrative staff," he said. Employes ranging from advertising executives to secretaries had been warned over the weekend to prepare to set props or unload trucks, and many appeared yesterday in jeans and sneakers instead of suits and dresses.

Many employes were even excited about the prospect: "It's fun to get backstage again," said Alex Morr. He and his wife, Judy, are the general managers of the Kennedy Center. Judy Morr said she had once done summer stock.

"It's amazing how many people have drama experience," said one Kennedy Center official.

Regarding the terms of the agreement, Ron Cocome senior-vice-president of the Instant Charge local, said they had won $5.12 1/2 an hour. But Martin Feinstein said the full-time and part-time wage was $5.00 an hour. Feinstein added that instead of a 15c per hour contribution to an annuity fund, the local had "opted for 12.5 cents in cash in their pockets." Other sources at the meeting said firmly that the terms of the agreement say $5 an hour for both full and part-time people.

Feinstein, after the meeting, commented "I don't think they're totally pleased and I don't think we're totally pleased. I don't think anyone walks away from the negotiating table with everything they want."

Cocome said, "I'm happy it's over." He said he and the other union negotiators were authorized by the local to give final approval to an agreement. "The people in that (Instant Charge) office are better off than they have ever been."

No matter the wording, the ballet should be dancing tonight. Everyone will return to work. "The trucks were supposed to be unloaded yesterday morning, so the pressure will be on," said Cocome, "but out stagehands can do anything." CAPTION: Picture, Strikers at the Kennedy Center, by James A. Parcell - The Washington Post