Environmentalists associated with former President Jimmy Carter are assailing what they call ''the almost total vacuum in US leadership in global resources, environment, and population'' of the Reagan administration.
Leaders of the Global Tomorrow Coalition, claiming 6 million members, voice alarm at the depletion of the world's resources and the threat of nuclear war.
In a speech and press conference Thursday, ruddy-cheeked Mr. Carter came close to a direct attack on his successor. Instead of following policies urged in the ''Global 2000 Report'' when he left office, Carter charged that ''our own government's actions, unfortunately, have been characterized by opposition to the recommendations (in the study).'' Emergency needs, he asserted, ''are now much more acute.''
Russell Peterson, president of the National Audubon Society and head of the Global Tomorrow Coalition, noted that Carter's final presidential address on Jan. 14, 1981, was ''the first time in history'' that a leader ordered an intensive study of the probable changes, 20 or more years ahead, in the world's population, natural resources, and environment.
''Although petroleum and other minerals are being consumed at a high rate,'' Carter said, ''the most acute pressures are on renewable resources, croplands, forests, fisheries, and water. Because of overuse of land and deforestation, the earth's 2 billion acres of desert will increase by 20 percent during the next two decades.
''At the same time, this year, there are about 90 million new people to feed and even more people will be added in each succeeding year - to a total of about 5 billion by the year 2000.
''By then each acre of arable land will have to support one-third more people. Previous faint hopes are fading that ultimate population will level off at about 10 billion.''
The issue of declining global resources marks one of the sharpest differences between the current and previous administrations. This was underscored earlier this week with the release of a report entitled Global 2000 Revised at the annual meeting of the American Association for the Advancement of Science in Detroit. The executive summary of this report, which was financed by the conservative Heritage Foundation, maintains that the conclusions drawn from the Carter administration report were wrong. Indeed, one author of the new study described the original Global 2000 summary as a politically motivated document that could be used to justify greater government control over natural resources and over efforts to monitor the environment.
''At this time,'' Carter said ''we can expect little help from the White House or executive agencies of government in dealing with worldwide problems that we must address.''
In a personal touch he recalled that when ''I left Carter's warehouse in Plains to campaign for president, we were selling a ton of 5-10-15 fertilizer for less than $40. Now the same product sells for more than $125.''
Prices of other chemicals have advanced in proportion, he said: ''Without any commensurate increase in crop prices, American farmers are struggling to bear this financial burden. Throughout the developing world these enormous price increases are more serious obstructions.''
Speakers linked the world's problems to exploding population. Population for the world was only 2 billion, Mr. Peterson said, ''when I went to college.'' Now , he said, ''We're adding the fifth billion in just 12 years.'' He noted that the first meeting of the global resources group was two and a half years ago and cited its rapid expansion despite what he called ''lost United States leadership.''
Carter recalled the shock of the first great oil price increase. At first, he said, ''an apparently unlimited supply of cheap energy helped to accommodate, and even to conceal, a disturbing growth in world population, overuse of resources, and degradation of our environment.'' But things changed abruptly, he said: ''Chemical fertilizers, improved pesticides, and irrigation steadily increased the world's production of food on roughly the same area of arable land.'' Prices rose.
''In some parts of the world, like Africa, food production per person is already showing a steady decline,'' he said.
Summing it up, Mr. Carter said, ''Unless we act together, the situation will inevitably get worse. In 17 years, global oil production per person is expected to be half what it was in 1979, and during this time we are likely to lose 30 percent of our tropical forests, 20 percent of plant and animal species, and several inches of topsoil. Deserts will expand. Carbon dioxide concentrations in the upper atmosphere are already warming the earth and melting the polar icecaps.''
Simultaneously, he said, ''acid precipitation is sterilizing our fertile lakes and streams and seriously reducing productivity of farmland.''