The fifth year of Major League baseball playoffs might not be enough to lure diehard Crimson fans from Harvard Stadium, but the post-season circus begins nonetheless today in Baltimore at 1 p.m.

In the American League, the Baltimore Orioles, Eastern division champs, will host the best in the west, the Oakland A's.

Later, at 4 p.m., the surging New York Mets will meet the team with the best win-loss record in baseball this year, the Cincinnati Reds. In Cincinnati's River-front Stadium, the Mets' righthanded ace Tom Seaver will face Red's righty Jack Billingham.

Both games will be televised on Channel 4.

Baltimore's Memorial Stadium will be the arena for the clash of two 20-game winners, with Oakland sending southpaw Vida Blue (20-9) against the O's righthander Jim Palmer (22-9).

The speedy Oriole offense that led the American League in batting in the second half of the season will not be full-strength today. Against a lefthander, manager Earl Weaver will bench Al Bumbry (.337) and Rich Coggins (.319), the second and third leading hitters in the American League.

Baltimore will play a right-handed team, with Earl Williams replacing Boog Powell at first and with Don Baylor, Paul Blair and Merv Rettenmund in the outfield.

Surrounded by rumors of his being named A.L. Most Valuable Player, Reggie Jackson, the powerhitting rightfielder for the A's, will be in top form for the contest. He hit 32 home runs and knocked in 117 runs this season, and his arm is the bane of many runners' lives.

Deron Johnson (.246), of Oakland, and Tommy Davis (.306) will be the designated hitters.