OH THAT JIM DINE, he's got heart. Hearts, actually, a great many of them, in various sizes and of various materials, now on view at the Hirshhorn, indoors and out. Big bronze hearts. Little bleeding hearts. Medium-sized mixed-media hearts. Hearts of steel and straw, etc.

Dine, you may recall, was one of those found-object and "happenings" folks who went to New York and invented Pop Art.

For a full quarter-century he's been hammering away at five themes: hearts, robes, tools, trees and gates. Some seventy of his works are in the show, including a pair of massive bronze hearts just off the truck from Walla Walla, Washington, where they were cast. The two big black hearts are titled, "Two Big Black Hearts."

What Dine's trying to say may not be immediately apparent to those unfamiliar with his work, but there's a 156-page exhibition catalogue ($35 hardcover, $22.95 softbound). The painting called "Coming in the Sun," for instance, features a six-foot acrylic heart with an old paintbrush stuck to it, an old lawnmower leaning against it, and a big old rock on the floor in front of it. The artist explains:

I had found an old lawnmower and used it for Coming in the Sun. The painting is about landscape and the way the sun felt on my body. It was the first time (1971) I used a single- image heart on this scale. Before that there were three double-heart paintings from the summer of 1970 in England, but they had a certain amount of insouciance which I would like to correct now because they weren't all that well observed.

If that seems a little less than clear, perhaps it's because Dine is, or used to be, also a poet. Let us turn to Martin Friedman's introductory essay in the catalogue. It says Dine's work "has undergone profound changes, shifting from ironic commentary on the everyday world to moody introspection," and that "over the last decade his paintings have assumed a gravity that borders on the ominous." In his final paragraph, Friedman punts:

"The full significance of Dine's themes remains elusive, even to him."

JIM DINE: FIVE THEMES -- Through April 28 at the Hirshhorn. L'Enfant Plaza or Smithsonian Metro stations.

JIM DINE: PART II -- Thursday February 28, and Saturday March 2, at 1 in the Hirshhorn auditorium. A half-hour film of the artist at work in London. Free.

JIM DINE: PART III -- Thursday March 7, at noon, and Saturday March 9, at 1 in the auditorium. An hour-long videotape of a 1978 interview with Dine. Free.