State Senate Republicans struggling to retain their slim majority are getting a sweet $1 million pre-Election Day gift from Mayor Bloomberg.

Sources yesterday said the mayor’s seven-figure contribution to the GOP Senate housekeeping account would show up in the next campaign filing with the state Board of Elections on Oct. 5, just a month before the election.

Bloomberg also chipped in $75,000 to the Independent Democratic Conference led by state Sen. Jeff Klein (D-Bronx), who has ties to Republican Majority Leader Dean Skelos and Gov. Cuomo.

The mayor has been the Senate GOP’s largest benefactor since taking office in 2002.