A special General Assembly conference designed to rein in the nuclear arms race ended today after five weeks, with little to show for the effort.

The outcome was anticipated by most diplomats, and some observers saw it as typical of U.N. forums--a vague blueprint for inaction, papering over the failure of consensus.

Yet many diplomats saw this failure as more damaging than most, dramatizing the collapse of an internatinal consensus on the theoretical goals of arms control that had existed for more than a decade and had been defined by the "action program" adopted by the assembly's first disarmament session, in 1978. In the interim the program had produced no action, which was one reason the second special disarmament session was convened on June 7.

Arms control activists, led by Mexican Ambassador Alfonso Garcia Robles, had hoped to promulgate a "comprehensive program of disarmament," which would go a step beyond the theoretical by defining a series of target dates for a comprehensive nuclear-test ban, limits on nuclear-arms production and deployment, the reduction of stock piles and a treaty banning the production of chemical weapons, among other prime arms issues.

In the past, despite the reluctance of the nuclear powers to be pressed on these issues in multilateral forums, there had been an activist and cohesive group of "middle powers" from the West and the Third World determined to elicit either grudging acquiescence or acute embarrassment.

This year, at a time when public awareness of the dangers of the nuclear arms race is far more intense, that core of activist governments has dissipated and Third World nations have fractured along East-West lines rather than press equally hard on Washington and Moscow for compliance with disarmament goals.

The conference organizers claim some success in public consciousness raising. A rally attracted an estimated 550,000 people to New York's Central Park on the first Saturday of the session. There also was intense press coverage of the speeches by governmental leaders such as President Reagan, Soviet Foreign Minister Andrei Gromyko, West German Chancellor Helmut Schmidt, British Prime Minister Margaret Thatcher and Israeli Prime Minister Menachem Begin.

Most of the speeches, however, restated disarmament formulas, without fresh ideas or follow-up. After the leaders left, the diplomats broke into working groups, where the specifics of the comprehensive disarmament timetable foundered in the face of objections from both East and West.

The only tangible result was the creation of a "world disarmament campaign"--a U.N. institutionalization of the drive to promote public awareness and concern about the arms race. Secretary General Javier Perez de Cuellar had opened the conference by pointing to the growing public awareness as "an encouraging phenomenon." He warned, "If we fail to rise to it, if we continue to temporize, there will be a massive disillusionment about the credibility of the professed allegience of governments to the aims of peace and progress around the globe."

Although the outcome surprised few diplomats, it upset the activists from 500 nongovernmental organizations who attended sessions and organized sideshows. Seventy-six of them issued a statement expressing "our sense of outrage" at the "obvious failure of this session," and called it "a betrayal of public confidence."