The Republican chairman of the Senate committee that handles civil service matters said yesterday he will oppose any White House attempt to cut the pay of federal workers to help reduce the deficit.

Sen. William V. Roth (R-Del.) said he expects civilian and military personnel, along with others, to make sacrifices to cut spending. But he said a pay cut for civil servants -- which is part of President Reagan's upcoming budget -- is not the way to make the savings.

Roth's opposition to the pay cut is very important. Many GOP senators take their cue on civil service matters from him because he chairs the Governmental Affairs Committee. The Reagan administration had counted on heavy support for the pay cut in the Republican-dominated Senate to offset opposition from Democrats who control the House.

Roth, a tough-minded conservative who can call in a number of IOUs from fellow senators, said most federal workers are "hard-working, dedicated professionals and we want to keep their talents and skills at work for the country." A pay cut, he said, could easily "drive the cream of the crop" out of government and create "monumental morale problems for those who remain."

He said personnel costs could be cut by changing or freezing future raises for civilian and military personnel and retirees, by delaying longevity step pay raises and cutting the federal work force via attrition.

Federal employes will get a 3 1/2 percent raise this month. But the White House will ask Congress to cut rank-and-file pay 5 percent next year. The Office of Personnel Management has said that if Congress rejects the pay cut, the only alternative would be to fire 125,000 employes. However the Office of Management and Budget, which makes up the budget for the president, says the firing option is not under consideration by anyone but OPM.

Roth's statement doesn't guarantee there will not be a pay cut but it certainly means the administration will have to work harder to get enough Republican and Democratic votes to approve the plan.