A suit challenging the constitutionality of the new "recapture" tax on property sales in Montgomery County has been filed in the circuit court by the county's board of relators.

The relators have been joined in the suit by Edward W. Schultze and the John C. Walker Realty Corp., both of whom had to pay the tax in selling properties recently. Enacted last September, the tax is paid on the difference between the selling price of a property and the last tax assessment figure, minus an examption of $8,000.

The rate of the recapture tax is $3.70 per $100. The tax on a property sold for $100,000 but assessed for only $80,000 would be figured on $12,000, for instance. The recapture tax for such a property would be 120 times $3.70 or $444.

The realtor group contends that the tax is illegal, regardless of whether it is property tax, a transfer tax or an excise tax. The realtors maintain that because only underassesses properties would be eligible for the tax, the law is discriminatory.

They also argue that the recapture tax is really a tranfer tax and point out that Montgomery County already has a maximum allowable transfers tax (1/2 percent) on real estate.