I. R. S. Defers Part of Its Ruling on Tax Exemption of Retirement Fund
IRS postpones port of its action until Aug 31; ruling is aimed at relieving burden on employers who contribute to fund and employees on whose behalf contributions are made; modifies earlier IRS ruling in relation only to employees; Cong and Ford Adm reptdly pressured IRS to rescind ruling; deputy White House press sec John Carlson denies that Ford Adm is involved in IRS action (M)