LET'S GET DEF: Geez, and we thought it took Fleetwood Mac a long time to make an album. Actually, next to Michael Jackson and Boston, the pokiest rock stars of the '80s have been Def Leppard, whose last album sold more than 6 million copies and spent 41 weeks in the Top 10 in 1983. The metal wonders are back--finally--with a new album, due out Aug. 3 from PolyGram Records, a mere 56 months since the band's last release. Titled "Hysteria," it includes such songs as "Women" (the first single), "Run Riot," "Pour Some Sugar on Me" and "Gods of War," which features excerpts from Ronald Reagan speeches (including the memorable boast: "For those of you who thought America would be passive--you were wrong"). Not surprisingly, the band jammed plenty of material into the album--it features 12 songs, clocking in at more than 62 minutes. . . . Meanwhile, R.E.M. (which has already released an outtakes album, a home video and sat in on the new Warren Zevon record this year alone) will release its new disc, "Document," in early September. Cut in Nashville, it features such numbers as "Exhuming McCarthy," "The One I Love" and "Finest Worksong."