On Election Day 1984, Missouri's Third Congressional District was in a melting mood, giving its heart in several directions. Reagan massacred Mondale there, 65 percent to 35 percent. But Reagan ran 35 percent behind the Democratic congressman, who was unopposed.

That man, Rep. Richard Gephardt, is one of the Democrats' fair-haired boys, literally and metaphorically. Folk wisdom is that red hair such as his indicates a volatile nature. Wrong. Gephardt militantly avoids militancy. His emotional equilibrium resembles that of Dickens' Lady Dedlock, who was so well-bred she could have ascended into Heaven without displaying -- indeed, without feeling -- any rapture.

He was not born with a silver spoon in his house, let alone his mouth. In the Depression, his parents, neither of whom had a high-school diploma, moved from a farm to St. Louis, where his father drove a milk truck. Today the father's son is considered (not least by his House colleagues) part of the cream that has risen to the top of the House. He may soon try to rise much higher. If Gary Hart and Mario Cuomo are the front rank of Democratic presidential candidates, Gephardt is in the front of the second rank, a promising place.

That is remarkable, considering that he is in the House. The Washington assumption is that God or (what is much the same) the Founding Fathers created the House to bore mankind. There are so many congressmen it is hard for any to become conspicuous. Conspicuousness is purchased in the coin of identification with splashy issues.

Gephardt first attracted attention -- and precious little of it -- by his attention to hospital cost-control. That issue is as recondite as it is important. Public attention to an issue is apt to be inversely proportional to its complexity and importance.

The House is not known as the Mother of Presidents. Only James Garfield went directly from the House to the White House. However, in 1976 Rep. Mo Udall (D-Ariz.) lost four primaries (New Hampshire, Massachusetts, Wisconsin, Michigan) to Jimmy Carter by fewer votes than Oklahoma's Sen. Fred Harris (quit pretending; you don't remember him) siphoned off from Udall's liberal base. Had Udall won even two of those primaries, he would have been nominated.

Qualities important in House leadership are different from qualities required of presidents. A House leader is a splendid spider, weaving a web that ensnares 218 members -- a majority. Gephardt becomes, for him, animated when describing the "thrill" of "getting 218." But getting there requires a legislative leader to rub the edges off issues, the better to build coalitions. Presidents must often lead by arousing passion to put edges on issues.

Legislators' lives are swallowed by meetings. Consider the Democratic Caucus, of which Gephardt is chairman (the fourth-ranking House leadership post). House leaders held 160 meetings just to cobble together support for Gramm- Rudman. Gephardt loves the House, but has seen the limits of life within what is, essentially, a 435-person committee. But his presidential prospects are threatened by the fact that he is guilty of, well, premature reasonableness.

In 1978 he opposed creation of a National Consumer Protection Agency. Today that idea seems as dated as William Jennings Bryan's free coinage of silver. Gephardt opposed federal regulation of used-car sales. He said: "I think it is insanity to think that the government can protect you from buying a bad used car." To many Democrats, this probably stigmatizes Gephardt as a heartless cad. But the governmental mentality he opposed -- patronizing and paternalistic government -- gave rise to the Reagan reaction.

Gephardt favored tuition tax credits when the budget permitted, and favors taxing some health- care fringe benefits. He opposes abortion, busing and additional gun controls. He has voted against an increase in the minimum wage, and against extension of the Equal Rights Amendment ratification deadline. As a presidential candidate, such votes might make him hard for some Democrats to swallow, but he would be hard for Republicans to handle.

As a leading advocate of tax reform, Gephardt symbolizes the transformation of American politics. Fifteen years ago, the Democratic intelligentsia was flirting with arguments for a "no- growth society." Today, Gephardt insists that encouragement of growth is the standard by which policies should be judged. He suits an era in which grasping reactionaries (Republicans) say the top tax rate should be 35 percent and seething egalitarians (Democrats) say it should be 38 percent.

Gephardt has just turned 45. He has three children, ages 15, 12 and 8. When the 15-year- old was two, the child had cancer. The three- year treatment, although successful, still has aftereffects. When asked how one runs for president without sacrificing one's family, Gephardt gives the only honest answer: "I don't know." The nation will be enriched if he discovers how.