“J. EDGAR HOOVER,” 8-10 p.m. Sunday, Showtime...

“J. EDGAR HOOVER,” 8-10 p.m. Sunday, Showtime (cable)--Footnotes.

They are what TV needs as much as anything, footnotes that certify the docu in modern docudrama, just as any worthwhile history book or biography is footnoted to signify credibility.

If TV dramatists are to play historian, then they should fulfill the obligations of historians. Primary and second sources should be listed . . . somewhere . Roll in footnotes with the closing credits, or insert them periodically, but include them . . . somewhere .

Awkward? Certainly. But necessary. How else can viewers of pay-cable Showtime fully assess writer-director-producer Robert Collins’ account of a man whose impact on the United States was profound and enduring?

“J. Edgar Hoover” needs more than mere footnotes, of course. It’s a flat profile that opens no doors, not even a crack, and sheds no light, not even a narrow beam. Its subject, played by Treat Williams, leaves us as he greets us, as a cold, steely, driven enigma, a blur of a man whose 48 years as FBI director become fleeting flashes.

It presents two hours of caricatures--Joe McCarthy, Truman, Eisenhower, Nixon, the Kennedys and L.B.J.--that pop up like wax dolls. The easiest target is Lyndon Johnson, depicted without essence and merely as crude and trashy. Collins shows him urinating on someone’s bushes. Moreover, Johnson, who was an enormous man, is played by Rip Torn, a smallish actor several inches shorter even than Williams.

Back on the footnote front, meanwhile, “J. Edgar Hoover” follows the familiar trail. Hoover’s shoddy attempts to discredit the Rev. Martin Luther King Jr. have been widely written about, and so have his differences with Robert Kennedy when Kennedy was attorney general under his brother John.

But was Hoover really the one who informed the younger Kennedy of President Kennedy’s assassination in Dallas? And if so, did he do it as callously as portrayed here? Hoover gets Kennedy on the phone and says only, “Your brother is dead.” Then he abruptly hangs up.

And so on and so on, as the biography of J. Edgar Hoover spills across the screen TV style, asking the blind trust of viewers.

Showtime airs “J. Edgar Hoover” again on Jan. 20, 24, 29.