Wrestling insiders know the prestige of the 19th Annual Cliff Keen Las Vegas Invitational (Dec. 1-2)--with many of its champions eventually reaching the NCAA finals the same year.      With a 2-0 dual record, Lehigh will make its 1st visit to Nevada since Dec. '94 and its fifth-ever.  One thing is certain: with 46 Top 10 wrestlers entered in 10 weights (a min. of 3 -- at 149-- and a max 6 at 125 and 197), every ranked entry is guaranteed at least one major test.  Three former NCAA champs will wrestle-- Stephen Abas, 125, Fresno St; Kirk White, now at 157, Boise St; and Brad Vering, Nebraska, 197, plus two top-ranked wrestlers--Adam Tirapelle, 149, Illinois and Otto Olson, 174, Michigan.        Top Teams entered:  #5-Illinois;  #7-Michigan;  #8 LEHIGH;  #9-Nebraska;  #11-Arizona St;  #13 Edinboro;  #14 Boise St;  #18 Ohio St;  #19-Oregon St;  #20-Pittsburgh.    ----------Details----------  19th Annual Cliff Keen Las Vegas Collegiate Wrestling Invitational Dec. 1-2, 2000 in Primm, Nevada (40 mi. S.of Las Vegas )  Tourney Location: on US Hwy 15; CA/Nev state line), in the Star of the Desert Arena, adj. to Buffalo Bills Hotel.  Times:  Fri, Dec. 1:  9:00 am (PST):  Prelims, Rounds 1 & 2, Consolations;   7:00 pm-Quarterfinals & Cons. Rds. 2 & 3  Sat, Dec. 2:   9:00 am--Cons. rd. 4;   10:00 am--Semis, Cons & Cons. Finals  5th, 6th, 7th, 8th;  5:00 pm--Finals, plus Cons. for 3rd, 4th  -----------------------------   While another 8th-ranked Lehigh team battles Delaware on Saturday in the Div. I-AA Football Championships, Lehigh Sports Communications will provide regular Las Vegas Tourney updates via traditional methods:  LU Hot-Line (610-758-5858);  LU Website (www.lehigh.edu; click "sports" then "SportsNews/Results") and at least 3 updates via direct email to our dedicated readers.  ------------------------------  The Mountain Hawk goals:  challenge for the team title and aim for individual wins over higher ranked wrestlers in each weight class.  A look at the large list of tourney entries which represents nearly half of the Div. I programs in the country.    NEXT LU HOME DATE:   Sat. Dec. 9--Sheridan Duals.  Rutgers (10 am);  Ohio U (12:30);  Boston U (3 pm)