If Congress is unable to pass a deficit reduction plan by the end of the month, scheduled across-the-board budget cuts will kick in, affecting both domestic and defense spending.
The National Science Foundation (NSF) today released a statement  from Director Subra Suresh explaining how the agency would handle the 5% cut in the funding it would receive for fiscal year 2013. The biggest impact: approximately 1000 fewer new NSF research grants during the fiscal year. "[T]here will be no impact on existing NSF standard grants," Suresh writes; all continuing grant increments would be awarded as scheduled.
NSF estimates that it awarded 7850 new research  grants in 2012, so for 2013 we should expect about 6850 new grants. NSF also estimates that in 2012, it supported some 40,885 graduate students  and 6935 postdoctoral researchers paid either through their principal investigators' research grants or, to a much smaller extent, on individual or institutional training grants. If we estimate that the average award lasts for 5 years, then approximately 8177 new graduate students and 1387 new postdocs were supported in 2012; if the ratios stay the same, then we can expect NSF to support 1601 fewer graduate students and 177 fewer postdocs in 2013.
(Speaking of the sequester: Our colleagues in Science's news department have created a hashtag on Twitter for posts related to science and the sequester, and a page  on their site to feature it. If you're on Twitter and tweet something about the effects of the sequester on science, use the hashtag #sciquester.)