President Reagan, saying the Democratic Party has deserted its traditional constituencies, charged yesterday that "it's no mere coincidence" that Democrats are strongest in "the most blighted areas of the country" and "places of desperation."

Reagan also briefly departed from his usual caution and predicted that Republicans may be headed for "an historic electoral realignment" on Election Day.

Using the White House as a campaign stage before his final 10-state political swing beginning Thursday, Reagan delivered a pep talk to 240 Reagan-Bush officials who have been recruiting blacks, Hispanics and other voter blocs this year.

"For longer than any of us can remember the Democratic Party has held the allegiance of a large number of Americans who were not well-served by the policies of that party," he said. "Yet, voting habits are hard to change. I know; I was a Democrat myself for most of my adult life."

Reagan said "a large number" of voters will cast ballots for Republicans for the first time next week. "Now this is no mere political cycle, nor has it anything to do with the personalities of the candidates. We're attracting the support of people who have never voted with us before -- not because they're deserting the Democratic Party, but because the Democratic Party has deserted them."

"For far too long now, the other party has taken for granted many of those who have faithfully given their support," Reagan said. "Big city machines kept in power by organized voting groups were key to the Democratic victories over the years. Yet, did these people find their lives improved by their unquestioned loyalty to the party?

"It's no mere coincidence that the most blighted areas of the country -- places of desperation -- are areas that have been political strongholds of the other party for many years," he said.

"Their policies are tax, tax, spend, spend, and no friend to those who want to improve their well-being. What the less fortunate need is not pity, but opportunity; not handouts, but jobs."

White House spokesman Larry Speakes refused to elaborate on Reagan's remarks. "I'll leave that at the other end of a 10-foot pole," he said.

Christopher J. Matthews, a spokesman for House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.), responded: "It is no coincidence that the man who ridicules the ghetto is the same man who signed the kind of restrictive covenants that helped create them."

Matthews said he was referring to recent news accounts that Reagan, in the process of buying and selling property in 1941 in Los Angeles, signed restrictive land covenants prohibiting the sale or use of land by non-whites, except for servants. The White House said later that Reagan was unaware of the restrictive covenants.

Reagan, who has courted Democratic voters this fall, has also stressed the need for more Republicans in Congress but refrained from specifically attacking Democratic members whom he may later need in congressional coalition-building.