Montgomery County budget chief Robert Kendal, at a packed public hearing last night, warned County Council members of dire financial consequences if they fail to enact the first step of a disputed plan to bring Montgomery's volunteer firefighting system under government control.

The county supplies money to pay about 700 full-time firefighters, all employes of independent fire companies that are controlled by more than 1,000 volunteers. Unless the council moves swiftly to reclassify those full-time firefighters as county employes, Kendal said, they will remain eligible for overtime pay under a recent federal court ruling.

That, he warned, could cost taxpayers up to $6 million in the next year.

Dozens of full-time firefighters, who would gain collective bargaining rights as county workers, jammed the council chamber in loud support of the plan, contained in a bill submitted by County Executive Sidney Kramer. Joining them were dozens of equally vocal volunteer firefighters, who view the proposal as a step toward the demise of their cherished, volunteer-run system.

The council has scheduled workshop sessions on the bill before voting.

Drawing on a study commission's recent report, Kramer, who was not present last night, has said he intends to make the firefighting system more efficient by bringing it under county authority. He said he would submit several bills this year aimed at accomplishing that, to the anger of many volunteers.

Although reclassifying the full-time firefighters as county workers is a part of Kramer's total plan, county officials sought last night to remove the current bill from the overall debate. They said it was being proposed ahead of other related bills because of the recent court ruling regarding overtime, and that it should be discussed only in that context.

Council member William E. Hanna Jr. disagreed. He called the July federal court ruling "the most fortuitous of circumstances" for Kramer, allowing him to advance the first part of his plan as an emergency.

Hanna called Kendal's financial projections "a fairy tale."

Comments similar to that drew loud applause from volunteers. Hanna prompted an equally loud response from paid firefighters when he said, "Well, I think I'll stop right here."

Council member Bruce Adams indicated he would support the current bill, but oppose any plan that would put the volunteer fire companies under the direct command of county officials.

U.S. District Judge Herbert Murray ruled July 30 that the fire companies are private entities. Citing the federal Fair Labor Standards Act, he said the full-time firefighters, as employes of private entities, must receive overtime pay when they work more than 40 hours in a week.

If the firefighters are reclassified as county workers, they would be considered public employes under federal law and would receive overtime pay only after working 53 hours in a week.

Murray has not yet calculated an overtime pay rate for the firefighters. But if they are not reclassified, Kendal said, based on the options available to Murray, "the fiscal year 1988 impact of the court's ruling will range between $1.7 million and $6 million. The fiscal year 1989 impact will fall between $1.8 million and $6.4 million."

And, he added, "county taxpayers will receive no more work hours of service for these extra costs."