For more than a decade, the Columbia Commuter Bus Corp., a transportation network devised and managed by Howard County commuters, has been an unqualified success--a cheap, efficient service for hundreds of workers who must make the 60-mile trek to and from Washington every weekday.

Started by a few car pool-weary commuters from Columbia, Md., the company grew from two buses in 1971 to a fleet of 18 last year, shuttling nearly 900 people from Columbia and Ellicott City to Washington regularly.

Today, however, the nonprofit bus line is on a rocky road, officials say. Ridership has dropped sharply in recent months and patrons have filed a record number of complaints about late and overcrowded buses, driving mishaps and poor bus maintenance. There is even talk of disbanding what was once a model of safe, reliable mass transit.

"We need to improve service drastically, and right away," said Iris Volkman, a company spokeswoman who has used the bus service since 1975 to get from her Columbia home to her job at the American Enterprise Institute in the District.

"A lot of people are leaving," Volkman said. "Some of them prefer their car pools to CCBC, if you can believe it."

CCBC is hurt most by competition from another commuter service--the dozens of van pools that ply Rte. 29 daily between Howard and the District, Volkman and other CCBC officers say.

"CCBC has never been in the business of making money," said CCBC president Phil Forest, "so when the state and the county support and organize van pools, they're eating into our ridership. The whole thing defeats the purpose of mass transit."

Some van pools, which offer tickets at half the price of Columbia's bus line, have "raided" CCBC bus stops for extra riders, Forest and Volkman said. "It's a bit unethical, to say the least," Volkman said. Van pooling, however, makes sense in Howard, where every day an estimated 18,000 commuters jam narrow country roads and major traffic arteries.

"I'm encouraging as much van pooling as I can," said Lu Clark, Howard transportation services coordinator, who has sparred with CCBC officials over the county's support for private- and public-sponsored van programs.

Nearly 400 Howard residents participate in the county's VanGo program, which has 32 12-seat vans leaving for the District each morning. CCBC has about 600 riders in 13 49-seat buses. The bus line, which makes stops at 55 Columbia locations and 26 District points, was scheduled to cut its fleet to 12 buses this week and to 11 for the summer because of ridership drops.

"Whether we cut back further than that is still unresolved," Volkman said. "There is the possibility of disbanding the service or seeking another contractor."

The Columbia line was patterned after a similar cooperative in Reston, Virginia's modernistic planned community. But while Reston's service eventually folded--Metro later assumed many of those local routes--CCBC thrived through a simple formula: charge riders just enough to pay the bus drivers and to keep the corporation afloat.

One-way ticket prices were inflated to discourage those riders; today, those tickets cost $4 each, while a 10-trip book is $25.50. With the purchase of a ticket, a rider becomes a "shareholder" in the corporation, which is run by 26 directors and several elected officers. CCBC buses are provided by Eyre Bus Service Inc. a company in Glenelg in western Howard County, under an annual $500,000 contract.

"It's truly a communal system," said Forest, 51, a retired government worker whose fellow travelers have established long-running bridge games on the evening trip home. "People take the bus service seriously."

But recent lapses in commuter comfort and the bus service itself have driven many riders away, officials said. In April, the company filed a report with Eyre Bus listing at least 150 service complaints ranging from "no air conditioning or interior lights to a driver who didn't know how to shift into first gear," Volkman said.

"Eyre Bus has failed us several times when buses showed up late or not at all," she added. "And some of those buses have been in very poor condition."

An Eyre spokeswoman said the firm's rapid growth in recent years had caused some problems with driver training programs. But she also said CCBC had failed to inform the bus company of schedule changes on several occasions.

CCBC and Eyre officials have scheduled a June 30 meeting between riders and bus drivers to discuss service problems.