Mayor Marion Barry yesterday requested approval to revise the city's fiscal 1983 budget and reduce congressionally authorized spending levels by $8.7 million to help avert a projected deficit.

The proposed changes, including cuts in budget authority for administrative activities, economic development, school transportation subsidies and pay increases, were contained in a "supplemental" budget the mayor sent to the City Council for action.

If approved by the council and Congress, the city's 1983 budget would be revised downward from $1,798,526,000 to $1,789,856,000.

In the past, the mayor has proposed supplemental budgets to raise authorized spending levels to take advantage of an unexpected rise in local tax revenues or additional federal assistance.

But this year's proposal attempts to reconcile the unhappy prediciment of declining local revenues and pressures on some agencies to spend in excess of the levels approved by Congress.

In a letter to City Council Chairman David A. Clarke, Barry noted that the current 1983 revenue projection of $1.77 billion is $23.8 million below original estimates.

"Clearly, no additional funds are available in fiscal 1983 to increase, or 'supplement,' the District's total appropriations," Barry said. "In fact, District-wide reductions have been and will continue to be required if budget balance is to be achieved in fiscal 1983."

The supplemental budget document unveiled yesterday offers few clues to the administration's progress in coping with a projection last fall of $110 million in revenue shortfalls and overspending.

The mayor has scheduled a press conference Monday to provide a mid-year financial status report.

Barry's proposed revisions for fiscal 1983 include net reductions of $2.7 million for governmental direction, $2.4 million for economic development, $1.7 million for public education (including $67,900 for the school transit subsidy program), $5.5 million for environmental services and $17.3 million for pay increases.

In reducing the budget for environmental services, Barry scrapped plans to transfer $5.4 million from the general fund to the financially ailing water and sewer fund.

The mayor also requested authority to raise the congressionally approved levels of spending by $15 million for public safety and $4.4 million for human services, to take into account additional spending pressures on those agencies.

Elizabeth Reveal, the mayor's budget director, said yesterday that the requested increase in spending for the Department of Human Services would have been substantially higher if the city hadn't reached agreement with 12 local hospitals to place a cap on total Medicaid reimbursements for the current year.

"Had we not had the maxi-cap agreement, we might have needed an additional $12 million to $13 million for Medicaid reimbursements," she said.

In his letter to Clarke, the mayor pledged to keep $20 million in the budget to help reduce the city's $296 million accumulated deficit.

"We fully anticipate that the $20 million reduction will be achieved, although doing so will require an additional $15.1 million in cost-savings between now and the end of the fiscal year if no improvement in the current revenue estimate occurs," he said.