A presidential advisory panel yesterday released five draft reports recommending ways to cut federal spending by more than $31 billion and increase revenues by more than $15 billion over three years.

In its second batch of cost-cutting reports, the President's Private Sector Survey on Cost Control said the government could save more than $9 billion by changing Medicare to a "prospective" system under which payments to hospitals and physicians are determined in advance. Such a plan for hospitals already has been approved by Congress as part of the Social Security bill passed this spring.

Yesterday's reports, written by task forces of businessmen working under the 161-member panel, covered the departments of Interior, Transportation and Housing and Urban Development, part of the Health and Human Services Department and the general subject of cash management.

The reports also recommended selling $900 million in public lands under the control of the Interior Department's Bureau of Land Management and imposing millions of dollars in new or increased user fees. The proposed user fee changes ranged from raising the price of a visitor's permit to a national park to recouping the full cost of Coast Guard services to boat owners.

The Reagan administration is under heavy fire for its plans to identify and sell "excess" public lands, including acreage held by BLM and the U.S. Forest Service of the Department of Agriculture. A proposed "user's fee" on boat owners, similar to that suggested by the survey, sank unceremoniously in Congress in 1981.

But industrialist J. Peter Grace, chairman of the survey, suggested that Congress, faced with an increasing federal deficit, might now be more receptive to a variety of budget-cutting ideas that have been rejected over the last two years. "How high does this deficit have to get before yacht owners pay for this?" he said of the Coast Guard proposal. "Things that were sacrosanct will get cut." Other draft proposals:

* Merging safety functions of the Federal Highway, Federal Railroad, Urban Mass Transportation and National Highway Traffic Safety administrations into a Land Transportation Safety Administration.

* Slowing payments to defense contractors, for $2.5 billion in savings and $15 billion in cash flow benefits. The report on government cash management identified $54 billion in such "cash acceleration" benefits, which it said could be used as a one-time deficit offset.

The survey has released 11 of its 38 task force reports, for a cumulative total of $86 billion in savings and $18 billion in new revenues. Because some of the savings are counted in more than one report, the final figures may be less than that, according to survey officials.

Of the $104 billion total in potential savings and revenues identified so far, Grace said $33 billion in savings and $9.2 billion in new revenues could be put in place without approval from Congress.