A succession of Howard County residents mounted a tumultuous 90 minute assault tonight on a proposed 20-year-development strategy for the county, telling officials at a public hearing that it threatens their neighborhoods and the region's rural character.

"I'm confused, harassed, upset and mad," said one county resident to the cheers and applause of the 150 people who jammed a school cafeteria for the first public hearing on Howard's proposed comprehensive zoning plan.

The plan, drafted by the county planning and zoning office, calls for sweeping changes in zoning regulations and establishes at least nine new categories for residential and industrial development.

Action on the 245-page document, parts of which were modeled on Montgomery County regulations, is not expected for many months.

At tonight's meeting--the first of three hearings scheduled to blanket this fast-growing county--speaker after speaker rose to denounce the zoning proposal as a "sell-out" to developers. The plan "includes the most outrageous proposals for change as demanded by the land speculators, developers and planners," complained Robert Solem, a resident of southeastern Howard for the past 15 years.

"I am not shocked. I am appalled," Solem said.

Most residents' objections centered on proposed changes in zoning regulations that would allow "floating zones" of low-density housing; a new category of medium-density housing that would give developers an option to build up to eight housing units per acre; and a new category of "planned employment centers", which residents charged would lead to projects other than the high tech parks and light industry now scattered along Rte. 29 in eastern Howard.

The zoning proposal also includes controversial new rules for transferring development rights and a proposal for "moderately priced dwelling units," two programs Montgomery County adopted many years ago.

"Anybody who drives Rockville Pike or Route 270 at rush hour in Montgomery County discovers those aren't the models we should follow," said Frank Salinger, a lawyer who recently moved to Howard County.

Gail Williams, a community leader in the Hammond area of southeastern Howard, said that if approved by the county Zoning Board, the new comprehensive plan would lead to "spot" zoning and a checkerboard of industrial and residential areas throughout Howard.

Williams, whose remarks were interrupted by applause from the audience, said the changes would "eradicate the quality of life we enjoy and expect . . . . It reflects the inputs of developers and not the citizens of Howard County."

Two Howard planners who attended tonight's meeting disputed Williams' charge that the comprehensive plan includes major deviations from the general development plan Howard County adopted in May 1982. Tom Harris, director of the planning and zoning office, and Robert McNamara, the plan's principal author, said the new zoning categories are consistent with the earlier plan.

Although the two officials responded to some direct questions from the audience, they responded to very few of the audience's complaints.