E. F. Hutton & Co. yesterday joined the growing list of brokers offering special services to shareholders in American Telephone & Telegraph Corp. who are unsure what they want to do with their telephone company shares after the company is broken up next January.

After January, in place of each share of AT&T they now hold, investors will receive one share of the new, smaller AT&T plus a share in each of seven new regional companies. The regional companies will be formed from the 22 local Bell-owned companies that AT&T must divest on Jan. 1.

The new Hutton offering will permit shareholders, prior to Jan. 1, to exchange each of their current AT&T shares for a new security called a unit trust, paying a one-time fee of 1.5 percent of the value of their current AT&T stock.

After Jan. 1, the unit trust will exchange current shares of AT&T it has received for the stock of the new AT&T company and the regional phone companies. Investors can exchange their unit trust shares for the new AT&T and phone company shares at any time.

There is uncertainty among investors and securities analysts about the future market value of AT&T and the newly formed firms. After January, AT&T will retain its long-distance, marketing, manufacturing and research arms. The divestiture of the operating telephone subsidiaries, such as the local Chesapeake & Potomac Telephone Co., was required by a 1982 antitrust settlement with the government.

A spokesman for the brokerage said that the trusts will simplify reporting and record keeping for AT&T owners. After Jan. 1, for example, instead of receiving quarterly dividend payments from one company, AT&T shareholders will receive quarterly dividends from eight companies.

The Hutton trust, like the Merrill Lynch's, will pay dividends monthly.

Hutton will not charge customers who exchange their trust shares for shares of the new AT&T and the seven operating companies before Jan. 1, 1989. Until that date, customers also could decide to cash in the trusts but sell some or all of the underlying stock without being charged commissions by Hutton, a spokesman said.

Owners of the Hutton telephone trusts can receive their dividends as cash payments as they would if they owned the AT&T stock directly. They also have the option of investing the dividends in any one of four Hutton money market funds, buying more units of the telephone trust or buying shares of a different "tax-advantaged trust."

A spokesman for Hutton said the tax-advantaged trust would permit AT&T shareholders to defer tax payments on the dividend income and convert the income from short-term to long-term capital gains. Long-term capital gains are taxed more lightly than short-term income.

Owners of the trusts will also receive regular reports on the divestiture process and on the status of the new, streamlined AT&T as well as the seven new operating companies.