The Montgomery County Office of Consumer Affairs has accused a Silver Spring home-improvement contractor of defrauding about 25 homeowners by failing to complete promised projects and violating an earlier consent order to refrain from deceptive and misleading trade practices.

In a 15-page lawsuit it filed recently, the county accused Stephen C. Sieber of false advertising, inferior workmanship and operating businesses under corporate charters that had been revoked by Maryland officials.

The complaint in Montgomery County Circuit Court also alleges that Sieber failed to perform warranty work and falsely stated that he employed registered or certified engineers in his firms.

The lawsuit named as defendants Sieber and several corporations, including Sieber Inc. Engineering and Construction and Thermal Installation Services.

Stephen Sieber denied the county's allegations. "They have ruined my company," he said. "I never walked off a contract or abandoned a job."

Sieber, who left the home improvement business last year after state officials refused to renew his license, said that under protest he signed a consent order in May 1989 with the county. Sieber said he has returned about $30,000 to customers as a result of that agreement and on his own to settle claims.

The lawsuit is seeking an injunction against Sieber to prohibit him from doing further home improvement work in Montgomery for three years and full restitution to aggrieved consumers.

George Rose, an investigator in the Office of Consumer Affairs, said the agency has received about 25 complaints in the past two years about Sieber's firms. Rose said Sieber failed to comply with the 1989 consent order that mandated refunds to consumers and a halt to alleged misleading statements. About a dozen county homeowners still have claims outstanding against Sieber, ranging from $7,000 to $94,000, Rose said.

The lawsuit said Sieber induced homeowners to pay him large sums of money for deposits on major remodeling or home-addition projects. One homeowner paid a $60,000 deposit for improvement work, Rose said.

The lawsuit contends that Sieber used shoddy materials and left many jobs unfinished. Rose, who inspected some of Sieber's projects, said, "It was the worst work I've seen in 16 years. There were code violations everywhere. The floors slanted every three feet. Roofs were held up with two-by-fours."

Potomac homeowner Carol Pinto said she paid Sieber $94,000 to add a sun room, install a new roof and build a deck onto a pool. "It's been a terrible situation," she said. Pinto said Sieber worked on the job for three weeks and then failed to return. "It will take a couple more years to complete the work he didn't do," she said.

The lawsuit also alleges that Sieber misrepresented the corporate status of his companies. The corporate charter for two firms, Sieber Inc. and Steve Sieber Construction Inc., were forfeited on Oct. 11, 1989, although Sieber continued to advertise and offer services under those names, the complaint said.