For the first time in 20 years, voter turnout increased in a presidential election. The increase, however, was well under 1 percent, far less than might have been suggested by this year's massive voter registration drives.

Although all the votes have not been counted, experts estimated that between 92 million and 92.5 million votes were cast, or between 52.8 and 53.1 percent of the voting-age population. In 1980, 52.6 percent voted, the low point in a steady decline since 1960.

The turnout figures show that Democrats fell far short of their goal of 100 million voters in 1984.

Although the turnout, when calculated as a percentage of the total population over 18, increased, it declined when calculated in terms of the number of registered voters.

A preliminary study by the Committee for the Study of the American Electorate found that turnout among registered voters fell sharply, from 75.2 percent in 1980 to 72.4 percent Tuesday. In 1960, 83.4 percent of those registered voted.

The decline in turnout among registered voters suggests that the $20 million or more that was spent on voter registration for this election succeeded in registering large numbers of people, but many of them failed to go to the polls.

ABC News exit polls showed that new voters supported President Reagan over Walter F. Mondale, 61 to 39 percent, compared with a 57-to-43-percent difference in favor of the president among those who had voted in previous elections.

The racial polarity of the electorate, with Reagan winning by wide margins among white voters and Mondale carrying the black vote to an even larger degree, was more pronounced among first-time voters than among those who said they had voted in earlier elections.

Ninety-five percent of blacks going to the polls for the first time voted for Mondale; other blacks favored Mondale, 88 percent to 12 percent. New white voters backed Reagan, 69 to 31 percent, while whites who had voted before supported Reagan, 62 to 37 percent.

The exit poll of more than 11,000 voters showed that blacks and Hispanics increased their percentage of the electorate only slightly, despite major efforts to increase registration among those two groups. From 1980 to 1984, the percentage of voters who were black grew from 8 percent to 9 percent, while Hispanics grew from 2 percent to 3 percent of the electorate.

Two separate studies of the returns suggested that the television networks' decision to declare Reagan the winner at 8 p.m. EST depressed turnout west of the Mississippi River, where polls closed two to three hours after the projections.

Curtis B. Gans, director of the Committee for the Study of the American Electorate, said a detailed state-by-state comparison showed that in western states where polls closed at 9 p.m. EST or later, turnout declined in 19 and increased in only six.

By contrast, he said, in eastern states where polls closed by 8:30 p.m. or earlier, 14 -- plus the District of Columbia -- had increases in turnout, and 10 had declines.

Illinois was the only state not accounted for.

A survey of 1,250 Oregon voters and nonvoters by William C. Adams, a George Washington University professor, "encountered a number of people who said that projections had a decisive influence on their decision not to vote," according to the author. "In many of our interviews, we received a lot of unsolicited complaints about projections."

In recent years, women have voted in significantly larger numbers than men, and Democrats had been hoping to capitalize on the vice-presidential nomination of Geraldine A. Ferraro to produce an even bigger turnout among women.

The ABC exit poll, however, showed men voting at the same rate as women, suggesting a decline in turnout among women.

A comparison of the 1984 ABC exit poll with the 1980 New York Times-CBS Election Day poll showed that Reagan's support among born-again Christians, a key GOP target group, grew. In 1980, they supported Reagan over President Jimmy Carter, 61 to 34 percent; in 1984, they supported Reagan over Mondale, 69 to 30 percent, a 12-point increase in the spread.

The born-again vote is a major force in two states where Republicans made significant gains in House contests: Texas and North Carolina, where 26 percent of the voters described themselves as born-again Christians.

North Carolina had the largest turnout increase of any state, 3.4 percent, according to Gans, but the District of Columbia had a 5.8-percent increase. Other states showing large increases were Virginia, 2.8 percent; Pennsylvania, 2.3 percent; Ohio, 1.4 percent, and New York, 1.3 percent.

The states with the greatest drop in turnout rates were Alaska, 9 percent, and Iowa, 9.4 percent despite a hard-fought Senate race.