The first signs of a "massive Democratic Party sweep in 1984" that may endanger President Reagan's reelection hopes and Republican control of the Senate are beginning to take shape "just below the surface in American politics," according to pollster Louis Harris.

The most recent Harris Survey, taken between Aug. 18 and Aug. 22, indicates that Democrats have wide leads over Republicans in House, Senate, gubernatorial and state legislative races, he said.

"Certainly, the hopes of the Republican Party that the Reagan 1980 election was a forerunner of a major change in the electorate for conservative Republicans akin to the New Deal revolution of Franklin D. Roosevelt in 1932 have now been shattered," Harris said.

" . . . Even at this early date, it would seem that the GOP will be lucky if it can avoid a disaster . . . in 1984," he said.

The findings include:

* Democrats hold a popular vote lead of 51 to 39 percent in 33 states that will elect U.S. senators next year. If Democrats retain this margin, Harris said it would be "virtually certain" that Republicans, who hold seats in 19 of the 33 states, would lose control of the Senate, where they now have a 55-to-45 majority.

* Democrats hold a 53-to-37 percent margin in House races, compared with a 56-to-43 percent margin in 1982 when they picked up 26 seats. This trend "could easily raise the Democratic majority in the House to well over 150 seats," Harris said.

Democrats hold 267 House seats and Republicans 165. There are three vacancies.

* Democrats have a 53-to-36 percent lead over Republicans in state legislative races and a 47-to-39 percent edge in gubernatorial races.

In a column describing the survey, Harris noted that Reagan continues to run almost neck and neck with the two Democratic presidential front-runners, former vice president Walter F. Mondale and Sen. John Glenn (D-Ohio) in most polls.

"But with a strong Democratic undertow in the offing in next year's elections at the state level and for both houses of Congress, there could be a kind of reverse coattail effect that will hurt Ronald Reagan's chances," he said.