President Reagan's proposed $9.8 billion cut in federal aid to cities and states would mean more layoffs by city halls around the nation, reductions in service and increased local taxes, the president of the U.S. Conference of Mayors said yesterday.

The proposed new Reagan cuts in aid to states and cities are larger than the ones he pushed through Congress last year. Those, which caused enormous furor, came in the end to $3.6 billion or 3.8 percent, according to budget documents published earlier this week. This year's cuts, by contrast, would come to 10.7 percent.

"The damage that the FY 1983 budget proposal would inflict on our cities and the suffering that it would inflict on so many of our citizens cannot be overstated," said conference president Helen Boosalis, the Democratic mayor of Lincoln, Neb.

Her declaration that the conference will oppose the cuts on Capitol Hill came three days after representatives of governors and state legislators announced similar intentions. State and local groups, which have been bitterly at odds over other issues, have scheduled a March 1 meeting to plan strategy.

Reagan has proposed major reductions in housing, job training, nutrition, mass transit and education programs. Boosalis said that when the impact hits city halls, mayors "would be pressured to increase regressive local taxes."

"But it also means that the people who are the victims of our current economic and social problems will see even less help, and even less hope, in the year ahead," she said.

Boosalis expressed particular concern about the proposed cuts because the White House has said it intends to freeze federal assistance to state and local governments over the next several years at the 1983 levels. The freeze would go into effect as control over federal programs is shifted to the states as part of Reagan's New Federalism.

Members of the mayors' conference, which is dominated by big-city liberal Democrats, were prominent in opposing the administration's first round of budget cuts last summer. The administration was so incensed at some of the rhetoric of Gary, Ind., Mayor Richard G. Hatcher, then the conference president, that he was excluded from meetings the president had with local government officials.

The administration sought to buy peace with the mayors this time around by sparing three aid and economic development federal programs--general revenue sharing, the Community Development Block Grant program and the Urban Development Action Grant program--from budget director David A. Stockman's ax. The mayors indicated strong support for these programs in a White House survey last summer.

The returns are not in on how well the White House succeeded in its efforts. Boosalis said she had not surveyed her fellow mayors.

John J. Gunther, executive director of the conference, said most of the calls he had received from members concerned cuts in federal programs aiding the elderly, but there also was concern expressed about reductions in spending for housing, health and nutrition.

Gunther said cuts in youth jobs programs and their consolidation with programs to aid Indians, migrant workers, veterans and the elderly worried some.

"Throwing elderly people in with youth to compete for money is not very nice," he said.