Top officials in Mayor Marion Barry's administration are considering the merger of several key District of Columbia agencies into a giant department of public works.

Sources said that the possibility of that merger played some role in the resignation Thursday of Transportation Director Douglas N. Schneider.

Although Schneider denied that in an interview yesterday, others close to Schneider said that the proposed merger, which they consider probable, was a key factor.

The new department of public works would consolidate the existing departments of transportation, environmental services, general services and surveys. With a total of 5,158 total authorized employes, it would be second only to the huge Department of Human Resources in the District government.

Carroll Harvey, director of the Department of General Services, a long-time associate of the mayor and the chief architect of the merger plan, said yesterday that he estimated the merger would save the District $9.2 million in the first year because of consolidated functions and a reduction in authorized personnel of 1,093.

Harvey said he has briefed City Administrator Elijah Rogers on the plan and is scheduled to give a detailed presentation to Mayor Barry soon.

A department of public works, he said, would put the District in the same organization posture as many other major cities.

Harvey was asked if he would be the director of the new expanded department, if it is approved. "I don't know," he said, "I didn't come here to do that."

Over at the Department of Transportation, several officials said that Harvey's plan played a role in Schneider's decision to leave this year. "The minute you start encumbering transportation with a lot of other programs you really can't be innovative," one well-informed official said. "And Doug enjoyed being innovative."

Schneider, a controversial figure in the city, was the author of the No Turn on Red sign and the massive parking ticket and towing program, among other initiatives he took to reduce traffic in Washington.

Schneider himself said, "I really don't want to get between this issue and the mayor; I can't say whether reorganization is right or wrong." He resigned effective in August, he said, "because I just have to do something else."

Schneider said he has no new job definitely in mind at this time, but that "I kind of like the idea of being in a private capacity," perhaps as a consultant.

I'm really interested in this urban transportation problem," he said, "and I'd like to work with other cities . . .I'm always interested in ideas, but down here you get bogged down in the day-by-day routine."

Schneider said he did not think his departure would lessen in any way the District of Columbia's commitment to the completion of the 101-mile Metro subway system. "My talks with Mayor Barry and others just don't lead me there," he said. "For one thing, it's obvious that the District of Columbia and downtown specifically is really benefiting" from the subway.