Prince George?Ûªs Independent Democrats renewed their attack on County Treasurer Charles E. Callow last night, charging that he failed to take advantage * of higher Interest rates in investing the County?Ûªs funds.</br></br>Vincent Femia, the Inde pendent opposing Callow ir the May 15 Democratic pri mary, said the Treasurer in vested $500,000 at County banks in ,1961 when Govern ment securities would have paid higher interest rates.</br></br>Femia, an accountant and lawyer, said Callow made two investments of $250,000 each on Feb. 1?ÛÓone in the Bank of Maryland and one in the Bank of Brandywine.</br></br>?ÛÏYet on these very same dates Government securities with the same maturity date wore available for purchase by this County paying an interest rate of 2.22 per cenL,?Û? Femia said.</br></br>The insurgent candidate also said the Treasurer?Ûªs office should not be ?ÛÏa part-time job.?Û? Callow has a private accounting business on the side.