The first privately offered issue of mortgage-backed securities sold out quickly last month.

On Sept. 21, Bank of America's $150 million offering of 8.375 per cent $25,000 minimum certificates representing shares in a pool of home mortgages was eagerly snatched up by institutional investors, market sources said.

Last week First Federal Savings and Loan Association of Chicago announced it had asked the Securities, and Exchange Commission for permission to offer $100 million in mortgage-backed pass-through certificates.

In related news the Chicago Board of Trad announced recently that Ginnie Mae futures contracts reached a record high during August. Nearly 62,000 contracts were traded, an increase of 78.4 per cent over the previous monthly record set in July.

This increased acitvity in the secondary mortgage market is seen by analysts as a way of insulating the housing industry against predicted increases in interest rates and by bankers as a means of increasing the supply of conventional mortgage funds at the same time.

Up to now the ability to issue mortgage-backed securities has been reserved for quasi-governmental organizations Offerings by the Federal National Mortgage Association Fannie Mae and the Government National Mortgage Association Ginnie Mae are based on government-backed or insured mortgages.

The largest secondary market in conventional residential mortgages is conducted by the Federal Home Loan Mortgage Corp (Freddie Mac). In 1976 it bought and sold $1.4 billion worth of mortgages. It issued $400 million in guaranteed mortgage certificates and $1.5 billion in mortgage participation certificates.

Private lenders traditionally have been considered too small to put together a pool of loans large enough to make a public offering based on it.

Last spring Bank of America, the nation's largest bank with deposits of $60.7 billion, applied for permission to become the first to do so. The final hurdle was cleared last month when the Internal Revenue Service ruled that the bank's pass-through securities can be considered investments in real property for tax purposes. (Interest and principal are "passed through" to the investor as they are received, usually monthly or semi-annually,)

By selling directly to the public, Bank of America expects to get a better return than it can get now by selling its mortgages at a discount to quasi-government bodies. In this way, the bank hopes to return more money to the residential market. The return on the first issue substantially exceeded Ginnie Mae's going rate of 8.02 per cent.

First Federal's offering will be made by a syndicate managed by Salomon Brothers. The certificates, in minimun denominations of $25,000, will be used to orginate new conventional residential mortgage loans without the institution having recourse to government programs.

National Thrift News see private-pool securities as the forerunner of a new, major form of money-market instrument. The trade publication notes, however, that there still are barriers to this type of financing, such as laws that bar mutual savings banks from buying the certificates or the requirement for first-hand inspection of property secured by a mortgage.

Trading in Ginnie Mae mortgage interest rates futures contracts began nearly two years ago. The purpose of trading mortgage futures is to shift the risk from lenders such as savings and loan associations of speculators. In return, the speculator have the possibility of making windfall profits on mortgage rates as some futures traders do on commodities such as soyabeans, silver, pork bellies.

Since the Commondity Futures Trading Commission approved them this spring, GNMA mortgage futures have been one of the fastest-growing commodities on the Chicago exchange, a CBOT statement reports, Aug. 24 volume of 5,600 contracts set a record. Open interest - the number of contracts not offset by opposite transactions or delivery - rose to 18,935 on Aug. 22, a sign of continuing faith in this market.

A GNMA futures contract calls for delivery of 100,000 principal balance of modified pass-through, mortgage-backed certificates.