A judge's decision that Maryland's definition of marriage is unconstitutional sent ripples through the State House yesterday, with politicians speculating about its impact on fall elections that are already shaping up as a defining battle between Democrats and Republicans. A revival of the dormant but divisive issue of gay marriage has the potential to rally conservative-leaning voters in an election year, political experts said. If the discussion leads to a constitutional amendment on the fall ballot prohibiting gay marriage - as some lawmakers want - Republican candidates such as Gov. Robert L. Ehrlich Jr., who is seeking re-election, and Lt....