This is the day when the politicians of Maryland stop talking about corruption and integrity and start thinking only in terms of votes - where they come from, in what quantities and how they add up to victory.

Around midnight tonight, after most of the votes are recorded, there will be one set of numbers and one set of winners. Until then, however, every candidate can and will look at the numbers in his own particular way and proclaim himself a winner.

Consider the election eve predictions of the four Democratic candidates for governor:

Acting Gov. Blair Lee III says he will stay even with his rivals in metropolitan Baltimore and use a 2-to-1 margin in the Washington suburbs to win the primary with at least 40 percent of the vote.

Theodore G. Venetoulis, the Baltimore County executive, says he will carry Baltimore City and his own county by 5 percent to 10 percent margins and cut into Lee's lead in the Washington suburbs enough to win the primary with 35 percent of the vote.

Harry R. Hughes, the former state transportation secretary, says he will get 50 percent of the total vote in Baltimore County, break even with Lee and Venetoulis in Baltimore City and win with 36 percent of the vote.

Baltimore City Council President Walter S. Orlinsky says he expects to carry Baltimore City and Howard County and stay close enough around the rest of the state to win a tight four-way race with 31 percent of the vote.

Obviously at least three of these four predictions will wash out before the night is over. The only things that can be said at this point with even a reasonable degree of certainty are the number of votes in the election and where those votes will come from, not to whom those votes will go.

Voting patterns in Maryland traditionally are analyzed in terms of five regions - metropolitan Baltimore, suburban Washington, Western Maryland, the Eastern Shore and Southern Maryland. Here is a region-by-region look at Maryland on primary election day: SUBURBAN WASHINGTON

The suburban counties of Montgomery and Prince George's are expected to provide about 25 percent of the vote in the state primary, with the Washington-oriented sections of Anne Arundel and Howard providing another 10 percent. In the Democratic primary, where state election officials expect about 500,000 votes will be cast, this region's vote total should exceed 180,000.

All of the polls indicate that Lee and his runningmate. Steny Hoyer, both of whom come from the Washington suburbs, will win at least a plurality and perhaps a majority of the vote in the Washington suburbs. Lee's campaign manager, Joseph Anastasi, is counting on a 2-to-1 margin here for his candidate.

Most of the voting anaylsts for the four candidates say that the suburban Washington vote will be of more importance this year than ever before. "With most other areas up for grabs," said Orlinsky, "the Washington area could be decisive."

The key factor in the Washington-area vote will be the turnout. In Prince George's, where Lee is considered strongest, turnouts historically have been among the lowest in the state. If that trend continues, Lee's edge there will be of minimal importance. Although Prince George's has almost 100,000 more residents, Montgomery has 30,000 more registered voters than its neighbor and traditionally, its voter turnout is substantially higher.

METROPOLITAN BALTIMORE

The Baltimore metropolitan region, consisting of the city, Baltimore Company, Harford County, Carroll County and portions of Anne Arundel and Howard counties, is expected to provide about 57 percent of the primary vote. Past elections show that the winner of this region has almost always carried the state.

In this primary, the voting preferences of the city and its suburbs appear more split than in the past, with Lee, Hughes and Venetoulis all having a realistic chance to carry the region.

The polls indicate that Lee is counting heavily on support from voting groups in the city - blacks and blue-collar workers - who traditionally have voted in low numbers. A high turnout there, exceeding 100,000, probably would help Lee more than his opponents. In Baltimore County, many of the areas with traditionally high turn-outs - such as Pikesville, Dundalk and Essex - have shown a trend toward Hughes, in recent weeks, according to newspaper polls. A high Baltimore County turnout - anything above 110,000 votes - would likely serve to Hughes' advantage.

In both the city and the suburbs, Venetoulis is hoping for low turnouts. "We've targeted our vote better than the other candidated have," said Venetoulis aide Steve Gelobter. "We know we'll get ours out. The fewer other people come out, the better for us." WESTERN MARYLAND

About 25,000 registered Democrats are expected to vote today in the Western Maryland counties of Allegany, Garrett, Frederick and Washington, providing about 3 percent of the statewide total. Lee is counting on the historically conservative voting patterns of the region to carry it for him. "We may lose Allegany, but nothing else," said Anastai. Venetoulis is relying on strong labor support in the industrial towns of Cumberland and Hagerstown, while Orlinsky is helped in the region by his running mate, Ronald Young, who is the mayor of Federick. None of the candidates is expected to pick up a substantial margin here. EASTERN SHORE

The people on the other side of the Bay Bridge, in Cecil, Kent, Queen Anne's, Caroline, Talbot, Dorchester, Wicomico, Somerset and Worcester counties, are expected to supply about 30,000 votes in the Democratic primary. Here, too, Lee is bolstered by the historically conservative nature of the voters. Hughes, a native of Denton in Caroline County, and Venetoulis, the only candidate who painstakingly has targeted votes in the region, are hoping to hold Lee's margin to a negligible level.

SOUTHERN MARYLAND

The counties of Calvert, Charles and St. Mary's on the western side of the Chesapeake Bay traditionally feature the highest voter turnout percentages in the state. In the 1974 primary, 54 percent of the registered Democrats in St. Mary's voted, which was 15 percent more than any other county in Maryland. With only 13,000 registered in the three counties combined, however, the Southern Maryland vote often his forgotten. The most popular politician in this region is Louis Goldstein, the state comptroller, who recently said that he was voting for Lee. A plurality of the region's Democrats is expected to follow his lead.