For the first time since enactment of the Voting Rights Act, young black voters turned out in higher proportions than young whites in last November's Senate and House elections, according to a voter-participation report released yesterday by the Census Bureau.

The study substantiated other analyses indicating that black voters played a pivotal role in Democrats' recapturing control of the Senate, particularly in Alabama, Georgia, Florida, North Carolina and Louisiana, where four incumbent Republicans and a fifth GOP hopeful championed by President Reagan were upset.

Political analysts said the study confirms a trend toward stronger participation by black voters, youths in particular. They credited Jesse L. Jackson, who has targeted black youths in his presidential campaigns, and a black backlash against the civil rights record of the Reagan administration.

The change bodes growing political influence, according to these analysts, as demonstrated by the near-solid opposition of southern Democrats to the Supreme Court nomination of Robert H. Bork, who is fervently opposed by black leaders.

"The strength of the black vote gave a lot of southern Democrats the political rationale to do what they wanted to do anyway" in the Bork vote, said Democratic pollster Geoffrey Garin, president of Garin-Hart Strategic Research Group. "It shows up on Election Day and on confirmation day."

Rep. John Lewis (D-Ga.), a civil rights leader elected to Congress last year, predicted that Jackson will win most of the new black votes on "Super Tuesday," the round of southern primaries and caucuses to be held March 8, bolstering his impact on the major Democratic primary contest of 1988.

"He'll carry the black youth voters solidly all across the South, partly to send a message to the old-guard leadership, but also to send a message to the present president," Lewis said. "I think there's a feeling among black young people that they missed the civil rights movement, and the vote is their instrument for social and political change."

According to the Census Bureau survey, young blacks, defined as those ages 18 to 24, trailed their white counterparts in voter turnout by about 10 percentage points until 1978, but their participation rose from 20 percent that year to 25 percent in 1982 and 1986. At the same time, turnout of young whites dropped from 24 percent in 1978 to 22 percent last November, the survey said.

Meanwhile, the gap between overall turnout of black voters and white voters was the smallest ever recorded -- 3.8 percent, compared to a 10-point difference in 1980. The turnout was 47 percent among whites, 43.2 percent among blacks.

"It's important because it tells you how much the country is changing," Garin said. "Black turnout used to be so much lower that there was a discount factor in assessing its impact. Nobody can discount it anymore."

Black youths topped their white counterparts in turnout last November simply by holding to their 1982 record, while white turnout declined. One striking decline has come among young and middle-aged white men, who had a turnout rate of 50.3 percent in 1966 and only 36.9 percent last November.

Overall, voter turnout decreased in November to 46 percent, compared to 49 percent in 1982, and black turnout fell from 49.9 percent to 47 percent. Against that backdrop, the consistent showing by black youth is considered significant.

"It's a tribute to Jesse Jackson," said Lee Atwater, campaign manager for Vice President Bush. "These are voters he's been targeting for the last four to five years, and I didn't realize he was as effective as he apparently was."

The Census study overstates voter participation because it is based on surveys, and people tend to be reluctant to admit they did not vote. However, its general trends are respected as valid.

Milton Morris, research director of the Joint Center for Political Studies, cautioned that black voter participation may soon begin to level off, following the gains of the last two decades.