LOS ANGELES, FEB. 24 -- Northrop was sued in U.S. District Court here today by four current and former employees for allegedly overcharging the government by more than $2 billion on the Stealth bomber program.

The suit, which is under seal in U.S. District Court here, alleges that Northrop overcharged the government on the program through a variety of false billings, misrepresented charges and double billings, according to Robert Kilborne, an attorney representing the employees.

As a result of the allegations, the Air Force Office of Special Investigations said it has started its investigation into the allegations at Northrop's Advanced Systems Division at Pico Rivera and Palmdale, two southern California cities where the Stealth work is performed. Such investigations by the Air Force are normally conducted in the event of this type of allegation.

"We just began an investigation," said Maj. Kathleen McCollom, an official in the Air Force investigation office. "We are looking at the Advanced Systems Division as a whole, which includes a number of different aspects and issues."

Officials at the U.S. attorney's office in Los Angeles are seeking classified documents from Northrop that the employees in the law suit assert will substantiate their allegations about the overcharges, Kilborne said. Air Force officials confirmed that the U.S. attorney's office is involved in the investigation.

Northrop spokesman Tony Cantafio said, "As a matter of policy, we cannot comment on the B2 {the Stealth bomber} or on every item of speculation that comes up on the program."

Los Angeles-based Northrop was awarded an Air Force contract in October 1981 for development of the top-secret Stealth bomber, which is intended to elude detection by enemy radar through a variety of new technologies.

The Air Force has said that it plans to build 132 Stealth aircraft at a cost of $36.6 billion in 1981 dollars. But the cost of the bomber has reportedly grown in recent years and some outside experts believe that the program will ultimately cost $60 billion.

The suit was brought under the False Claims Act, which enables individuals to sue on behalf of the government and share in the ultimate recovery of any funds owed the government.

For Northrop, the new Stealth bomber lawsuit comes after troubling litigation against the company for its role in producing guidance equipment for the MX missile. The company is facing civil fraud charges brought by the government last year and it is known that a federal grand jury is conducting a criminal investigation into its MX work.

In addition, the company is facing three other false-claims suits brought by former and current employees represented by Kilborne and Herbert Hafif, the attorneys who have become regular opponents of Northrop.

The new Stealth bomber lawsuit contains 17 counts or allegations of violations under the False Claims Act, Kilborne said. The suit was sealed, and thus could not be examined by reporters, because under federal law the Department of Justice has 60 days to decide whether to join the plaintiffs.