Health spa owners in Virginia, in a sweat over a state law that requires each club to post a $50,000 bond to protect customers of failed businesses, got a break from the General Assembly yesterday.

Despite cries from Sen. Wiley F. Mitchell (R-Alexandria) that a new bill "guts" a year-old law, the Senate approved a sliding bond scale ranging from $10,000 to $50,000 depending on how many members belong to the spa.

The bill, introduced by Del. Kenneth R. Plum (D-Fairfax), author of last year's measure, also sets a bond ceiling of $150,000 for any one firm that operates several spas.

Mitchell failed to get the Senate to place a cap of $200,000 on spa bonds. "The bill you have before you is a bad bill . . . . It was written by the health spa industry," he said.

The bill has passed the House and now goes to Gov. Charles S. Robb, who, a spokesman said, has yet to take a position on the measure.

Plum said he decided to seek changes in the law after a survey showed that about 80 percent of spa customers pay monthly fees, which limit their liability, rather than pay one-time memberships the bonds are supposed to protect.

The new bill also requires spas for the first time to register with the state and requires spa owners to place any advance membership funds in a state-controlled escrow account until the spa has been opened at least 30 days.