The D.C. Wage-Hour Board voted yesterday to require minimum $3.90 hourly earnings for security guards, furniture movers, certain truck and cab drivers, construction workers and swimming pool lifeguards -- the highest government-set pay floors for any groups of employes in the nation.

Heeding a warning by carwash operators that their industry would be imperiled, the board backed off from its proposal to set an identical $3.90 minimum wage for their workers. It decided instead to require minimum earnings of $3.65.

The board also set a $3.75 minimum wage for day laborers and theater ticket-takers and ushers.

Currently the District-set minimum wage for such workers is $2.75 an hour, set in 1975. However, most now earn at least $3.35, the current federal minimum wage. The federal minimum generally applies whenever it exceeds the District's wage floor.

The increases will take effect Oct. 31. Richard R. Seideman, executive secretary of the wage board, estimated that about 15,000 workers will receive pay increases as a direct result of the wage order. Uncounted thousands of others already earning above the legal minimum also may get raises because many employers maintain the pay gap between them and lower-paid workers.

The $3.90 wage will become -- narrowly -- the highest government-set minimum wage in the nationa. Currenlty the highest is a statewide $3.85 for all workers in Alaska.

Under District law, the Wage-Hour Board sets differing minimums for nine different catagories of workers. Currently the highest minimum is $3.75 that went into effect last year for beauty and barbershop workers.

In yesterday's order, the board noted that its task is to set a living wage for the "working poor," generally nonunion workers living at the subsistence level. It noted that a single individual living alone would require at least $4.48 an hour to subsist.

The required hourly earnings of at least $3.65 for carwash workers includes 15 cents in tips. Employers are actually required to pay a minimum of $3.50 an hour. Only if the carwash worker receives less than 15 cents an hour in tips will the employer be required to make up the difference. If the employer chooses not to deduct tips, he or she must pay $3.65 an hour.

The board's order requires employers to keep track of the amount of tips reported to them by their workers.

At a hearing last month, executives of parking garage companies testified that -- although they currently are permitted to do so -- they never have deducted tips from the pay of their employes, and that to begin such a practice might cause confusion and dissension.

Such deductions for tips also are permitted employers of bootblacks, beauticians, barbers and hotel and restaurant service workers.

In yesterday's order, the wage board also set minimum wages of $3.35 for those employed under the Youth Employment Act and the federally subsidized CETA jobs program, for learners during their first six months of work and for full-time students employed by the colleges they attend.