A REAGAN SECOND TERM will pose a real threat to three programs of vital interest to city governments. The President wants to reduce deficits without increasing taxes and will turn to spending cuts. The President has made clear his dislike for intergovernmental aid and has shown his specific disdain for programs which provide direct aid to cities rather than through some state mechanism. The three vulnerable programs are:

*General Revenue Sharing, first enacted in 1972 with the support of President Richard Nixon, which provides $4.6 billion each year to local governments to use to meet local priorities. GRS was to ease the burden on the property tax;

*Community Development Block Grants, first enacted in 1974 with the support of President Gerald Ford, provide $3.5 billion each year for city developments and services which primarily benefit low- and moderate-income persons. CDBG replaced urban renewal and model cities programs to encourage greater local flexibility; and

*Urban development Action Grants, enacted in 1977 and the only new domestic program put in place during the administration of President Jimmy Carter, provide $400 million each year for public development funds to cities in economic distress to leverage private job creating investment.

All three of the programs have been used to assure job-creation and economic expansion through public/private partnership efforts, and to shore up social services which could not be provided by local governments.

Even though the economic development and private sector job creation intents of these programs appear to be in line with the Administration's philosophy, Republican mayors were unable to win endorsement of it from the platform committee at the August national convention of the GOP. Indeed the words "city," "town," and "urban" do not appear in the 1984 Republican Platform.

AS DAVID STOCKMAN IS now putting the budget together for the President to send to Congress next January, he must be desperate in the search for areas to cut He is locked into expenditures beyond even his cutting reach--interest on the national debt, social security, military, civil service and veterans' pensions, and the President's commitments to defense and agri-business Therefore the $8.5 billion in annual outlays for GRS, CDBG and UDAG are a tempting target.

Stockman, who had opposed all of the programs as a member of the House of Representatives, persuaded Mr. Reagan to eliminate the UDAG funds in the first budget he sent to Congress in February 1981. That decision was reversed only by a face-to-face appeal to the President and his aides Edwin Meese and James Baker by a dozen mayors. These mayors and their colleagues not present at the meeting, but whose support was enlisted in an intense lobbying effort, stood together, Republican and Democrat. Such unity of purpose among the mayors, regardless of Party, was not evidenced again as Reagan cut back on social programs and urban aid during the remainder of his first term.

Bipartisan stands by mayors against federal action contrary to the interest of cities are not unprecedented. Mayors of both parties stood together to challenge proposals of Presidents Roosevelt, Eisenhower, Johnson, Nixon and Carter. In 1965, the U.S. Conference of Mayors expressed opposition to President Johnson's proposal to move water pollution programs from the Department of Health, Education and Welfare, where mayors were pleased with its administration, to the Interior Department, where its urban orientation might be lost. The President called Mayor Daley, Chicago's powerful political leader, and asked him to tell me, the lobbyist for the nation's larger cities, to back off. The mayor refused the President's request. Again, in January 1979, when President Carter and his staff were angered at my public analysis and criticism of the deep cuts in urban programs proposed in the 1980 budget, the executive committee of the Mayor's Conference--three-fourths of whom were Democrats--refused White House requests to repudiate our staff work and endorsed the analysis and the criticism.

BUT THE REPUBLICAN PARTY under Reagan runs a very tight ship--witness the unanimous vote of House Republicans for the budget reductions and tax cuts in August 1981. Will the Republican mayors, and there are many of them (35 percent of the cities with a population of more than 30,000 have Republican mayors), stand up in 1985? Certainly George Voinovich of Cleveland and Richard Berkley of Kansas City, two of the nation's leading Republican mayors, will continue to fight for these programs.

Unemployment, homelessness and hunger remain serious problems in cities. The national economic recovery has not closed the employment and income gap for minority youth and displaced workers regardless of race. Federal aid is the tool with which cities can address such problems. Unless the mayors overcome partisanship and stand together, and this may mean open and public disagreement with Mr. Reagan, the chances are that federal aid to cities will be an early victim in next spring's gun vs. butter (or even margarine) war.

John J. Gunther executive director of the United States Conference of Mayors since 1958, is currently a fellow at the Kennedy School of Government's Institute of Politics.