A fire described by investigators as suspicious in origin caused substantial damage early yesterday to offices of the top executives of the Western Development Corp. in Georgetown.

No cause has been determined for the blaze, but a D.C. Fire Department spokeswoman described it as "maybe arson, maybe not." The fire, which apparently started in an office on the top floor of the firm's headquarters in a century-old building at Wisconsin Avenue andM Street NW, was reported at2:42 a.m. and was extinguished within 19 minutes, she said.

Fire officials estimated the damage at $50,000. But John Lemon, a contractor hired by Western to start repairing the offices, said that the damage could total $200,000.

No one was injured.

Western is one of the city's more controversial developers and frequently has been involved in disputes about its proposals, particularly its construction of Washington Harbour, a massive commercial and condominium complex that is nearing completion on the Potomac River shoreline in Georgetown.

The firm developed the Georgetown Park shopping mall across M Street from its offices and has won the right to develop the Market Square site at Seventh Street and Pennsylvania Avenue NW.

Stacy Hornstein, Western's vice president for operations, said that while fire officials called the blaze suspicious: "It just appears to be a normal fire. It's an old building."

He said the fire appeared to have started in the office of Anne Mastin, a leasing offical for the firm, and that the heaviest damage occurred there. The fire was confined to the second floor of Western's offices, which are located above the Georgetown branch of the National Bank of Washington.

The fire blew out a skylight, burned through the walls and ceiling near Mastin's office, and caused substantial smoke and soot damage to the offices of Western Board Chairman Herbert S. Miller and the firm's president, Thomas J. Regan Jr. Several pieces of office equipment were destroyed or damaged.

Hornstein said many employes were able to continue work in other areas of the company's offices yesterday and corporate officials had asked him to try to get the damaged offices repaired by Monday.