American Telephone & Telegraph Co. Chairman Charles L. Brown expressed optimism last night that the Bell System and the Reagan administration ultimately would sign a divestiture plan that would meet the approval of U.S. District Judge Harold H. Greene.

"I find it hard to believe that we're not going to be able to surmount this final hurdle," Brown said only a day after Greene ordered AT&T and the Justice Department to revise the historic Jan. 8 divestiture plan so that greater protections would be given to AT&T's emerging competitors and local telephone customers.

The divestiture plan would require AT&T to spin off its 22 wholly owned local telephone companies. In return, AT&T no longer would be barred from entering the computer business, and the government's eight-year-old antitrust suit against AT&T would be dropped.

Although Greene embraced the overall concept of divestiture, he said he would not sign the plan unless his changes were adopted.

"It would be very frustrating" if AT&T and Justice couldn't work out an acceptable agreement for the judge, Brown said.

Appearing on the MacNeil-Lehrer report, Brown indicated that AT&T would not be adverse to many of the changes Greene has ordered, including his request that AT&T be banned from the electronic publishing business for at least seven years.

"This is almost a non-issue with us," he said.

Nor was Brown upset that Greene wants to play a much more significant role in overseeing the divestiture than AT&T and Justice had called for. 'I find it hard to believe that we're not going to be able to surmount this final hurdle' -- AT&T Chairman Charles L. Brown

"I don't think that surprises us or disturbs us," he said.

Brown also did not seem bothered that, contrary to the divestiture plan, Greene wants the divested local telephone companies to keep the lucrative yellow page business.

However, Brown noted in an interview after the show that he had serious concerns about Greene's directive that local companies be allowed to sell telephone equipment in competition with AT&T.