NEW YORK — It’s not only the murdered Cordelia that John Lithgow bears onto the open-air stage of the Public Theater’s “King Lear.” All evening, this big, winning lug of an actor also has to carry an excessive amount of the poignant weight of Shakespeare’s tragedy, in a production that does too little to lighten his burden.

Lithgow’s emotional accessibility is an attribute employed to distinct advantage in director Daniel Sullivan’s visually appealing, three-hour mounting of the play, especially in its later phases, after Lear is stripped of dignity and sanity, and is left to writhe in the mire of his monumental folly. Among all the characters implicated in the play’s horrors, however, Lear too often comes across here as the only one capable of a response with the requisite intensity. The absence of a compelling depth of feeling is particularly apparent in two other pivotal performances, those of Annette Bening, as Lear’s soulless eldest daughter, Goneril, and Clarke Peters, portraying Gloucester, the blinded nobleman in “Lear’s” mirroring subplot, about another father catastrophically misjudging his children.

As a result, the “Lear” that had its official opening Tuesday night — the first “Lear” according to the Public Theater, to be presented in the park’s Delacorte Theater in more than four decades — successfully finishes only a portion of its harrowing journey, as the mechanics sometimes shift disconsolately into neutral. Only the potent relationships forged with the king by two of his loyalists — Jay O. Sanders’s satisfyingly jaunty Kent  and Steven Boyer’s touchingly perceptive Fool — suggest anything like the bonds of a real family. By contrast, the dark hearts of Lear’s elder offspring, Goneril and Regan (Jessica Hecht), and the more valiant one of the youngest, the misprized Cordelia (Jessica Collins), remain on this occasion muscles in need of more definition.

Lithgow, then, has less to react against than some luckier Lears; the tempests triggered by his daughters have nothing on the maelstrom that the spiritually damaged  king encounters on the heath, in a storm on a bare platform conjured impressively by set designer John Lee Beatty, lighting designer Jeff Croiter and video designer Tal Yarden. And yet the actor does not let this deter him; his reflexive fury at the indignities heaped on him by Goneril and Regan, and Regan’s husband, Cornwall (Glenn Fleshler), transforms in Lithgow’s countenance convincingly into bewilderment, confusion and despair.

His descent into the abyss almost complete, this Lear has a moving respite, in his brief reunion with Cordelia, before she’s executed under orders of Gloucester’s viciously double-crossing younger son, Edmund (Eric Sheffer Stevens). (Chukwudi Iwuji gives a livelier account of Edmund’s nobler brother, Edgar.) It’s at Lear’s lowest moment that Lithgow’s performance reaches its peak; you can’t help but feel for the regal breadth of the monarch’s loss as he cradles the only child who treasured him. A belated grasp of the cruel end to which he’s led his daughter is etched in Lithgow’s haunted gaze.

Although the rewards of Sullivan’s “Lear” are unevenly distributed, Lithgow’s stirring turn ensures the tragic center holds.

King Lear, by William Shakespeare. Directed by Daniel Sullivan. About three hours. Through Aug. 17 at Delacorte Theater, Central Park, New York. Tickets are free and distributed in the park and online. Visit