Howard County transportation officials will recommend Thursday that Columbia residents pay a special 2 1/2 cent tax to save their community's deficit-ridden bus system, the chairman of the county's public transportation board announced today.

Robert L. Shipley said that designating Columbia a "local tax district" would cover the huge annual deficits of the 15-year-old ColumBus transit system, which is now scheduled to lose its funding by spring 1985.

"Support on the board for the special tax district is virtually unanimous," said Shipley, who headed a task force that recently concluded a year-long study of Howard's mass transit needs. The task force's recommendations, including the Columbia transit tax, were expected to win easy approval at a transit board meeting Thursday night.

If approved next year in a county-wide referendum, the transit tax would add at least 2 1/2 cents to the Columbia property tax rate, Shipley said. The 18,000 households in the planned community already pay 75 cents per $100 of assessed valuation for local services.

Shipley said the tax would help keep ColumBus solvent as Columbia's population nearly doubles to 100,000 over the next decade. Other officials, however, expressed doubts that the tax would be approved in a referendum.

"A transit tax is a good idea, but I just don't know how palatable it would be to people outside Columbia," said Pamela J. Mack, chairwoman of Columbia's local governing council. "I think the people who are served by a bus system--teen-agers and the elderly especially--would be content with a tax."

In the past 15 years Columbia has spent roughly $2 million to subsidize ColumBus, Mack said. In 1981, however, the Columbia council voted to end the subsidies--and effectively kill the system--by April 1985.

Despite 17,000 riders per month, the eight-bus system is operating at a $60,000 annual deficit, officials said.

"Columbia is more supportive of a tax than the rest of the county," said Lu Clark, the county's transportation services coordinator. "But even in Columbia, the transit tax is not overwhelmingly accepted."

For years, neighboring jurisdictions have used transit taxes to defray bus system costs. Montgomery County approved its Mass Transit Facilities tax in the late 1960s, and the county-wide assessment has paid for the county share of Metrobus and rapid transit costs, as well as deficits in the local ride-on bus program, a spokesman for the county transportation department said.

In addition to the transit tax, the Howard transit board was also expected to recommend the merger of the ColumBus system with the Urban-Rural Transportation Alliance, a bus system that serves the elderly, handicapped and poor throughout the county.

Shipley also said the public transit board would recommend that the county fund a commuter transit system between Howard and Washington and between Howard and Baltimore.