Following tentative settlement of the 17-day-old nationwide telephone strike, the C&P Telephone companies yesterday resumed negotiations with the union representing 32,000 of their employes, who could return to work as early as Thursday if local contracts are also settled.

Tentative agreements must be reached by midnight Wednesday at all 34 local telephone bargaining units around the country in order to send back to work the 675,000 employes striking American Telephone and Telegraph Co. nationwide. If all local units settle by the deadline, then all of AT&T's unionized employes will return to work Thursday, pending a final vote by mail ballots in September to approve or reject the national and local contracts.

"Nobody can settle locally unless everybody settles locally . . . . Nobody goes back to work unless we all do," said George R. Strick, vice president of District 2 of the Communication Workers of America (CWA), which represents employes of the four Chesapeake & Potomac companies in Maryland, Virginia, West Virginia and the District of Columbia.

CWA officials who approved the national contract Sunday said yesterday they believed they had won significant improvements in job security to protect workers from having jobs eliminated or downgraded because of new technology. They said they were hopeful that this and other added benefits would lead to approval of new contracts at the 34 local units.

Picketing continued yesterday at dozens of AT&T and C&P offices in metropolitan Washington, but the ranks of the picketers were diminished because of the news of the possible settlement and because many strikers have taken temporary jobs as the strike entered its third week, union officials said.

CWA and C&P officials yesterday were optimistic that local contracts would be successfully concluded, pushed along by the prospect that a local stalemate could hold up the nationwide return to work. "Both sides are feeling the pressure" to settle, said Strick, whose bargaining committee resumed negotiations with C&P at the Shoreham Washington Hotel yesterday afternoon.

Neither the union nor the company would discuss specifics of the negotiations, but the unresolved local issues include pay differentials in various metropolitan areas, job descriptions, and the company's practice of evaluating and disciplining operators based on silent monitoring of their calls and clocking of their speed in handling calls.

Under the proposed three-year national contract, wages would increase 5.5 percent immediately, and then a combination of cost-of-living raises and "productivity increases" is expected to raise wages by 16.5 percent by the end of the three years, according to estimates by CWA.

But wages were considered a secondary issue by many employes who were more concerned about having their jobs eliminated or "de-skilled" because of computerized technology, union officials said.

"My first concern is keeping my job and getting as much training as I can get" to adapt to new technology, said Tony Tranfio, 36, an engineering assistant who has worked 14 years for C&P. As he walked a picket line at 20th and L streets NW, Tranfio said the union appeared to win a significant victory in getting the phone company to agree to pay for a $30-million program to retrain and relocate workers affected by new technology.

"I think the strike was worth it," said Nelline Dickerson, an AT&T data processing clerk who said she is concerned about being replaced by new computers. "If we hadn't gone out on strike, I don't think we would have gotten protection."