Federally insured savings and loan institutions took in $3.6 billion in new deposits in July, the largest monthly gain in more than two years, the Federal Home Loan Bank Board said. The July gain in net deposits was the largest since May, 1985, and only the second gain in 11 months. Net deposits in July were 24% greater than in July, 1986. In June, customers withdrew $2.8 billion more than was deposited. This followed a gain in net deposits of $1.6 billion in May and eight consecutive months in which withdrawals were greater.