The owners of Atlanta's "city-within-a-city" Omni International complex continued last-minute negotiations this week, trying to restructure their debt and stave off a threatened foreclosure next Tuesday.

The $100 million complex - containing a 500-room luxury hotel, nearly 500,000 square feet of office space and dozens of shops and restaurants - is under of threat of foreclosure by a group of banks led by New York's Morgan Guarantee Trust Co.

Businessmen here say one possibility is that the Omni International Ltd., a partnership of about 30 investors owning the complex, will seek protection under the federal bankruptcy laws.

However, an Omni International official claimed that there is a "very high probability" that a settlement will be reached before the foreclosure deadline, adding that a bankruptcy petition is "one of the least likely" possibilities.

The Omni complex, one of Atlanta's two financially troubled modern megastructures, nestles between the cityowned Omni coliseum (home of Atlanta's professional basketball and hockey teams) and the state-owned World Congress Center convention building on the fringes of downtown Atlanta.

The structure, which houses a popular skating rink for lunch-hour enthusiasts, is the brainchild of developersi-Tom Cousins and Maurice Alpert.

Perhaps a central irony of the Omni International's money woes is that so many of its tenants have become financially successful. The hotel, one of the fanciest in town, reported a 90 percent occupancy rate for February, and the retail operation is conceded to be faring well.

However, several factors contributed to the present situation. Sources in the business community point to cost overruns, slow leasing of the office space and - most dramatically - to the collapse of the complex's ambitious indoor amusement park, the World of Sid and Marty Crofft.

The park, a $20 million high-rise project with an eight-storey escalator and several rides, closed down in 1976 after less than six months of operation, and its space has been vacant eversince.