A presidential advisory council said yesterday it had found ways to save nearly $48 billion in government spending over three years, largely through sharp cuts in federal employe benefits.

The proposed savings were contained in draft reports by six of 38 task forces working under the President's Private Sector Survey on Cost Control, a controversial panel of 163 private businessmen headed by industrialist W. Peter Grace.

"Our principal goal has been the improvement of systems and management procedures," said Grace. "We brought the expertise of the private sector to bear on the operations of government."

Grace said the panel expects to recommend $60 billion or more in savings when all the reports are assembled and a final report is sent to the president in late June.

But many of the savings identified yesterday are along the lines of budget cuts already achieved or proposed by the Reagan administration. Some of the recommendations are identical to proposals the administration failed to get through Congress last year or the year before.

The task force report on the Agriculture Department, for example, says nearly $7 billion could be cut from the federal food stamp program, a program that has grown by 45 percent since 1980 despite the administration's repeated efforts to rein it in.

The task force said $1.7 billion could be saved by counting school lunch benefits as income in determining eligibility, an administration proposal Congress rejected in 1981. Counting child nutrition benefits as income could save more than $500 million, the task force said. Congress rejected that idea last year.

Among the task force's new ideas is a $3.4 billion savings that it says could be achieved by changing the standard household size used to calculate benefits. Smaller changes, including eliminating the $10 minimum monthly benefit and improving "economies-of-scale factors," could save $1.6 billion more, the task force said.

Nearly $35 billion of the savings identified yesterday would come from federal employe benefits, an area that has already received considerable attention from the administration in the last two years.

The largest chunk of savings identified by the task force on personnel management, $16 billion over three years, would come from changes in the civil service retirement system.

The draft report suggested setting 62 as the normal retirement age for federal employes, who may now retire with full benefits at 55 if they have at least 30 years' service. It also suggested penalizing workers who elect to retire early, and changing the way annuities are calculated. Reagan's fiscal 1984 budget already contains the latter two provisions.

The panel said $4.8 billion could be saved by changing the civil service classification system and downgrading some positions, and more than $7 billion in savings could result from changing the way annual leave and sick leave are calculated.

Although Grace referred to the proposals as "management savings" that would not eliminate government services, administration officials acknowledged that many of the recommendations would involve policy changes.

"Any time you change a benefit formula, that's a policy change," an Office of Management and Budget official said, referring to the standard household size used to calculate food stamp benefits.

The Grace panel, appointed by Reagan last June, recruited 1,300 other private businessmen to staff task forces that fanned out over more than 60 federal agencies in search of ways to make government more efficient.

The six thick volumes released yesterday represented the first of their reports, which will be considered in public hearings over the next three months.

The draft reports contained the caveat that the recommendations "do not take into account political, social or economic conditions" that may affect the administration's ability to support them.

But Grace said he expects Reagan to give all of the recommendations a fair hearing at the White House. "I'm convinced that he sincerely believes in this effort," Grace said, noting that Reagan appointed a similar private-sector task force as governor of California and adopted 1,600 of its 2,200 recommendations.

In other recommendations, the task forces suggested:

* A 40 percent reduction in the staff of Action, the government's volunteer agency, for a $27 million saving.

* That the Commerce Department's National Oceanic and Atmospheric Administration sell the right to market its satellite data, for a revenue gain of $500 million. That proposal also is making its way through the administration independent of the Grace panel.

* That the Department of Energy "improve operation and reduce unnecessary costs" in the Strategic Petroleum Reserve, a $1.3 billion saving.

* A general phasing out of a broad variety of Environmental Protection Agency grants to the states to help them meet pollution-control laws. Such grants programs have been trimmed in administration budget requests for the last three fiscal years.