(Charles Dharapak/AP)

TWO OF Northern Virginia’s three congressmen — Frank R. Wolf, a Republican, and James P. Moran Jr., a Democrat — are retiring after long tenures. There are spirited, expensive races to replace them.

The 8th District, which extends west through Arlington to Tysons Corner and south along the Potomac through Alexandria and Springfield to Woodbridge, is dominated by Democrats; despite various travails, Mr. Moran never faced a tight race for reelection.

A strong and experienced Democratic candidate emerged from last spring’s party primary: former lieutenant governor Don Beyer. He would make a fine member of Congress, and we support him. A former ambassador to Switzerland and Liechtenstein, Mr. Beyer is knowledgeable about foreign affairs. Closer to home, he has been involved for decades in issues including teen pregnancy, high school dropouts, poverty and welfare reform. He has committed himself to grappling with climate change, about which he speaks with understanding and passion.

Mr. Beyer’s Republican rival, Micah Edmond, a retired Marine Corps officer with policy experience on Capitol Hill, is also an impressively substantive candidate. Having served on the staff of the Simpson-Bowles commission, he has a detailed command of the nation’s fiscal challenges, and he has shown guts in straying from GOP orthodoxy on some issues. For example, he wants to raise the federal gas tax to support highway construction, and he supports extending legal status to the millions of undocumented immigrants in this country.

Either man would make an effective lawmaker. We believe Mr. Beyer’s breadth of experience in state, national and foreign policy makes him the better choice.

Unfortunately, the 10th District offers a mirror image; we find ourselves unable to endorse either candidate. The district includes parts of Fairfax and all of Loudoun counties and other points west past Winchester and Front Royal. The race there, to replace Mr. Wolf, has been a largely negative contest between Del. Barbara Comstock (R) and John Foust, a Democratic member of Fairfax County’s Board of Supervisors.

Ms. Comstock is an energetic campaigner, but on a range of policies she has taken hard-line positions at odds with the interests of many Northern Virginians. Mr. Foust has been a solid supervisor — he knows the county budget, and he played a constructive role in promoting Metro’s Silver Line extension — but shows no spark as a campaigner and no deviation from party talking points.

In the early 1990s, Ms. Comstock worked for Mr. Wolf, whom we regularly supported for reelection. He was a conservative by any measure, but one who never took compromise off the table. By contrast, Ms. Comstock, in her four years in Richmond, has been the sort of inflexible politician that has led Congress to paralysis. One of a minority of GOP lawmakers who signed a pledge opposing new taxes under any circumstances, she voted against a bipartisan bill last year to pay for improvements to Virginia’s chronically underfunded road and rail system — the first new transportation money in a quarter-century. She did so in spite of her own party leadership’s pragmatic support for the bill.

If Ms. Comstock wins, we hope she recasts herself in Mr. Wolf’s mold, for another partisan warrior in Congress in the last thing voters need.

In District 11, Rep.  Gerald E. Connolly is the lone incumbent seeking reelection in Northern Virginia. A former chairman of Fairfax County’s Board of Supervisors, Mr. Connolly, a Democrat, is a dominant figure in Northern Virginia politics; few people are as well-versed and effective in addressing the problems of federal workers.

He faces only a nominal challenge from Republican Suzanne Scholte. She has done admirable work promoting human rights in North Korea, but on many other issues she is not well-versed.