Two companies that provide most of the bus service to local airports have filed for protection from their creditors under Chapter 11 of the federal bankruptcy code, but airport and company officials said yesterday that they don't expect a disruption of service.

Airport Baggage Carriers Inc., based at Baltimore-Washington International Airport, and its subsidiary, The Airport Connection Inc., based at National Airport, filed documents Dec. 30 with the U.S. Bankruptcy Court for the District of Maryland.

Chapter 11 protection allows a company to continue operating while developing a plan to repay creditors.

The privately held companies owe $326,013 to their top 20 unsecured creditors, according to the documents filed with the bankruptcy court.

"There has been no break in service, and there won't be," said Mordecai Buckingham, director of airport operations for The Airport Connection, which provides scheduled bus, van and limousine service to National and Dulles International Airport.

The companies do not plan to lay off any of their 300 employes, he said.

"We just need a couple of months to get our feet on the ground," Buckingham said of the two companies, which together carry about 900,000 riders a year to and from the three airports.

The Airport Connection is one of five companies that operate under the name "Washington Flyer," providing ground transportation to the two Virginia airports under a contract with the Metropolitan Washington Airports Authority, which operates National and Dulles.

The company accounts for about 75 percent of the Washington Flyer business; other companies provide the Washington Flyer taxi service, according to Richard Griesbach, the authority's business manager.

Airport Baggage Carriers provides ground transportation to BWI from the District, Baltimore, Towson and Hunt Valley, Md., with vans and buses bearing the BWI name and logo.

The company has a contract with the Maryland State Aviation Administration.

Although National and Dulles once subsidized ground transportation service, the companies now pay concession fees to the airports. The service generates $2,800 a month in fees to the aviation administration, and $1,000 a month to the airports authority, airport officials said.

Both companies are profitable, Buckingham said. The problem was the eight money-losing months of the limousine service to National that started May 1, he said.

Buckingham said the companies plan to reorganize, pay off their debts and continue service.

The airports authority is taking no chances, however.

National and Dulles officials have prepared a contingency plan to take over operation of the Washington Flyer bus service if Airport Connection finds it cannot continue, Griesbach said.

The company's contract with the authority expires April 30, 1989, so the authority could award the contract to another company by the end of the year and request that it begin service early, if necessary, Griesbach said.

BWI monitors the service closely and is generally pleased, said deputy airport administrator Nicholas Schaus.

"We have seen no service problems," he said. The contract at BWI does not expire until 1994.