Deposits at savings and loan associations exceeded withdrawals in October for the first month since February, thanks to All Savers certificates, U.S. League of Savings Associations President Rollin D. Barnard said yesterday.

Barnard said the league's preliminary data indicate deposits exceeded withdrawals by $2.1 billion last month, with Americans depositing $18.7 billion in All Savers certificates at S&Ls during the first month the certificates were on sale. He said 25 percent of the money deposited in the certificates was new money; the remainder was transferred from other accounts.

The Federal Home Loan Bank Board also released figures yesterday estimating All Savers deposits for October at $17.1 billion. It said that between 10 percent and 15 percent of that sum was new money. Sales started out strong, with $11.6 billion sold in the first 10 days. Less than half the amount was sold in the next 20 days. At the beginning of October about 30 percent was new money, but almost none of it was after that, the FHLBB reported.

Meanwhile, assets of money market funds grew $443.2 million in the week ended Wednesday, down from the recent heated pace, but still maintaining an average weekly growth of $2.2 billion for 1981. Average yields decreased.

William E. Donoghue, publisher of Donoghue's Money Fund Report of Holliston, Mass., said the average seven-day yield on funds fell to 14.87 percent from 15.08 percent, while the average 30-day yield came in at 15.30 percent, down from 15.43 percent.

The Investment Company Institute, a mutual fund industry group based in Washington, said broker-dealer funds grew $353.2 million and general-purpose funds grew $370.4 million. Funds catering only to institutions had an outflow of $280.4 million.