REP. GOODLOE E. BYRON, who died suddenly while jogging Wednesday night, was a congressman who tended to constituents' problems and reflected their views with the same singleminded dedication that he devoted to marathon running. In four terms, he showed little interest in innovating, exercising leadership or aquiring influence within the House. Indeed, he shunned controversy to the point of leaving the Commerce Committee, with its energy and public-health concerns, after his record on environmental issues had come under fire.

In many states and seasons, such an incumbent would have been challenged by a Republican who combined similar middle-of-the-road views with more agressiveness. Particularly, one might have expected some such show of fighting spirit in the Sixth District, one part of Maryland where the GOP has retained some strength. Mr. Byron was preceded in Congress, after all, by two Republicans, Sen. Charles McC. Mathias Jr. and former senator J. Glenn Beall Jr., now his party's candidate for governor.

But the Republicans decidedit wasn't worth the effort - that Mr. Byron was unbeatable. And now, of course, they are paying, in embarrassment, for their defeatism. With no credible candidate in the primary, the GOP nomination went by default to one of the state's perennial fringe candidates, a scuffy Baltimore indigent named Melvin Perkins. Mr. Perkins has just spent a week in the Baltimore County jail and paid a fine for assaulting a female bus driver. He has no visible means of political support. But he does have the congressional nomination and seems disinclined to give it up.

After Mr. Byron's death, some state Republicans mumbled about mounting a write-in campaign for someone else. But that would be hard to do in four weeks in a district that uses voting machines. Western Maryland GOP leaders therefore conceded the seat and endorsed Beverly Byron, the congressman's widow, whom the Democratic central committee nominated Thursday night.

It is the story of the Republican Party - a bit extreme, perhaps, but illustrative nonetheless. Notwithstanding its professed intent to rebuild its base and recruit attractive new candidates, the GOP is still strangely reluctant to contest many seats and to protect itself against contigencies such as an incumbent's death. To make much progress in Maryland - or nationwide - the Republicans have to start challenging a lot of amiable but unexiciting Democrats.The GOP won't always win - but losing after an honest effort has got to be more inspiring than losing, by default, with the likes of Melvin Perkins.