WASHINGTON, June 10— The rise in carbon dioxide and other gases in the earth's atmosphere will have an earlier and more pronounced impact on global temperature and climate than previously expected, according to evidence presented to a Senate subcommittee today.
Scientists and senators at a hearing by the Environmental Pollution Subcommittee agreed that the dangers of manmade changes in the atmosphere had moved from hypothesis to imminent reality and must be addressed quickly.
They said the rise in temperatures was expected to cause profound climatic changes and raise sea levels substantially.
Witnesses at the hearing also testified that the ozone layer of the upper atmosphere, which protects the earth from the sun's ultraviolet light, is being rapidly depleted by manmade gases, and the increased ultraviolet radiation would result in a rise in skin cancer cases and other ecological damage.
Dr. James E. Hansen of the Goddard Space Flight Center's Institute for Space Studies said research by his institute showed that because of the ''greenhouse effect'' that results when gases prevent heat from escaping the earth's atmosphere, global temperatures would rise early in the next century to ''well above any level experienced in the past 100,000 years.'' Steeper Rise in Next Century
Average global temperatures would rise by one-half a degree to one degree Fahrenheit from 1990 to 2000 if current trends are unchanged, according to Dr. Hansen's findings. Dr. Hansen said the global temperature would rise by another 2 to 4 degrees in the following decade.
While the effect of small increases in global temperature is now unclear, Andrew Maguire, vice president of the World Resources Institute, a Washington research and policy group, said that the doubling of atmospheric carbon dioxide that is foreseen would cause a rise of 3 to 8 degrees in temperature by the 2030's. He said this would devastate agriculture in the United States and elsewhere, and would cause a rise in sea level of some 4.5 feet as polar ice melted.
Earlier projections of warming trends had held that they would not occur before the middle of the next century. One of the reasons that scientists now expect faster and higher temperature rises is the emerging consensus that gases other than the carbon dioxide emitted by the burning of such fossil fuels as coal are playing a major role in the greenhouse effect.
The greenhouse effect is the name given to the phenomenon created when carbon dioxide, methane, chlorofluorocarbons and other gases accumulate in the atmosphere and prevent radiant heat from the sun that has reached the earth's surface from escaping back into space.
Dr. Hansen and other scientists testifying today said there was now broad consensus among scientists that the greenhouse effect was speeding up the increase in global temperatures. Less Urgency in 1983
In 1983 a report by the National Academy of Sciences said the greenhouse effect was a ''cause for concern,'' but concluded that there was time to prepare for its impact.
The academy report projected a doubling of greenhouse gases by the third quarter of the next century. Dr. Hansen's research, however, found that if there is no change in the current rate of growth, the greenhouse gases would double by the late 2020's.
A report by the Environmental Protection Agency three years ago said the warming trend could start by the 1990's and could reach as much as 4 degrees Fahrenheit by 2040, but this was attacked by President Reagan's science adviser at the time, George A. Keyworth, as ''unnecessarily alarmist.''
Today, the scientists and the senators on the subcommittee asserted that there must be national and international action now to mitigate and deal with the imminent effects of the atmospheric changes taking place as a result of human activity. Chafee Asks Early Action
Senator John H. Chafee, the Rhode Island Republican who is chairman of the subcommittee, quoted a recent assessment by the Department of Energy, which said, ''Human effects on atmospheric composition and the size and operations of the terrestrial ecosystems may yet overwhelm the life-support system crafted in nature over billions of years.''
Senator Chafee said it would be too risky to wait until all the answers about atmospheric changes were known before taking action.
He called for the Reagan Administration to take up the issue at the next international economic summit meeting and also at the President's next meeting with the Soviet leader, Mikhail S. Gorbachev.
While the scientists testified today that it would be some time before there was enough data to pinpoint regional climatic changes, it was considered likely that some of today's most productive agricultural areas would become too arid for farming.
They also testified that a ''hole,'' in which the ozone has been reduced by some 40 percent, has formed in the ozone layer over Antarctica.
While many aerosol uses of chlorofluorocarbons have been banned in this country, their use in other applications is increasing, and they continue to be used in aerosols in other countries.