Barack Obama’s support from blacks and young people has intensified during his five-month slog through the Democratic primaries. Hillary Rodham Clinton has grown ever stronger among the elderly, especially older white women.

Exit polls of voters showing the strength of support for each candidate underscore the challenge facing Obama: As he shifts his focus to a likely general election against Republican John McCain, he must maintain the loyalty of longtime supporters while winning over Democrats who have been reluctant to budge from Clinton.

The primary voting ends Tuesday with contests in South Dakota and Montana. A look at exit polls from 33 previous primaries where both candidates competed shows that in a race with few major policy differences, each has patched together coalitions of racial, social and ideological groups that have cemented.

A few groups, if anything, have developed progressively stronger attachments to their candidate.

In primaries held through Super Tuesday, Feb. 5 _ the day Obama showed his ability to win contests around the country _ the Illinois senator was getting an average eight in 10 votes among blacks. That was a commanding advantage that included the 78 percent he got from blacks in South Carolina, the first state on the calendar with significant numbers of black voters.

Yet as sniping between the two candidates’ camps made race a more polarizing factor, Obama’s support from blacks grew even stronger. In primaries since Super Tuesday, he’s gotten the votes of nearly nine in 10 black voters.

“I think it’s due to his religion” and the controversy over his former pastor, Rev. Jeremiah Wright, said Yulonda Howe, 46, of Los Angeles. She said the black community understands that “on some things you can disagree with your pastor.”

Obama has also seen his support grow among voters under age 30. In contests through Super Tuesday his average advantage with them was 17 percentage points, while since then his average edge has been 27 points.

Obama’s growth with young voters has been even sturdier among whites under 30. Their support for him grew from an 18-point margin through Super Tuesday to 38 points in later primaries _ including a 60-point edge last month in Oregon, a hotbed of progressive college campuses.

Clinton has won growing support from older voters, especially white women. Whites ages 65 and older supported the New York senator by an average 28-point margin through Super Tuesday, and 39 points since then.

Her edge among older white women has averaged an enormous 45 points since Super Tuesday. That is up 9 points from the earlier contests and includes margins exceeding 50 points last month in North Carolina, West Virginia and Kentucky.

“She comes the closest to what I believe” on leaving Iraq and sparking the economy, said Jan Haus, 66, of Scottsdale, Ariz. “She knows what to do around the White House.”

Working-class whites and whites who said race was an important factor in choosing a candidate also leaned toward Clinton by stronger margins after Super Tuesday, as have white men. That could be because there were more Southern and rust-belt states, where whites were more likely to back Clinton, in the later contests than in the earlier ones.

Charles Franklin, a political scientist and authority on polling at the University of Wisconsin, said the candidates’ performances with voting blocs in particular states can vary according to the strength of their campaigns locally and each state’s overall ideological tilt. But he said the historic nature of this year’s Democratic race _ pitting a woman against a black for the nomination _ also had a big impact.

“The uniqueness of the candidates almost demanded that there would be this demographic division,” Franklin said.

A candidate’s performance with blocs of voters in primaries does not necessarily signal what will happen in the general election, when voters are more focused on issues and their own partisan loyalties. Early polls pitting Obama against McCain show varying results on who is ahead among white women and older voters.

The data comes from interviews with more than 44,000 voters in the Democratic primaries in the 33 state primaries where both candidates competed. The margin of sampling error was plus or minus 1 percentage point, larger for some subgroups.