Today's pop quiz: is there any appreciable political difference between the following two vignettes from the evening news? Scene A: with America's most recognizable residence clearly visible in the background, the correspondent signs off this way: "Judy Woodruff, NBC News, at the White House." Or Scene B: same correspondent, standing outside a college building festooned with candidate banners and bunting, offers this complimentary closing: "Judy Woodruff, NBC News, with the Carter campaign in Philadelphia."

Unfortunately, we will not know the correct answer for at least several weeks and quite possibly not until early November. The apparent thinking of President Carter's political brain trust, headed by the canny Bob Strauss, was that the second scene, variations of which we will all be able to view in our neighborhoods very soon, would be the bigger help to the president's reelection campaign.

From the country's (rather than the campaign's) interest, the president's decision to emerge from his isolation is all to the good. We all need reintroduction and communication. The president needs to confront and to understand both the anguish and the melancholia of the people he leads in the summer of 1980. And we need to understand better where the president proposes to lead us, and why.

Here in Washington, where no inheritance tax is levied on unearned cynicism, the early returns on the president's decision to leave the White House are in. Once again, goes the prevailing opinion, Jimmy Carter has demonstrated his electoral genius: that he knows a lot more about running for president than about being president.

The judgment in this precinct is that Carter may have made a political mistake in his decision to leave the White House. Back to the Quiz, he is now Jimmy Carter, presidential candidate, and no longer Jimmy Carter, the president. On the evening news, we will be treated to scenes of the president campaigning before crowds just as Edward Kennedy, Ronald Reagan or George Bush do. Like their crowds, Carter's crowds will be alternately bored and enthusiastic, boisterous and indifferent. The stamp "presidential," which all reports from the White House, regardless of their substance, bear, will be missing.

By returning to the country, the president loses control, in some degree, of the campaign dialogue. Everything is fair game now, from abortion to his earlier membership on the Trilateral Commission. It is probably only a matter of time before the president is picketed by unemployed auto workers or the wives and children of the hard-hit (by elevated interest rates) craftsmen of the building and construction trades. Mini-cams will let us know as soon as it happens. In a matter of weeks, or broadcasts, Jimmy Carter, the commander-in-chief, will be Jimmy Carter, the front-runner campaigning in Sacramento or St. Petersburg today. Film at eleven.

Carter is leaving the best campaign platform in the United States, the White House, where he has had a veritable parade of visitors. But, as almost anyone who has been there would admit, the most apoplectic business or labor leader turns into a pussycat in the house where Lincoln agonized and Roosevelt rallied a nation. Whether it's the setting or just the history, very few presidents face cross-examination on their court. Their interrogators are usually intimidated.

The inept handling of the announcement of Carter's decision to leave the Rose Garden probably tarnished the president's most indispensable political asset: his perceived integrity and honesty. But the damage was not severe. However, the decision, and the way it was botched, almost certainly encouraged the slightly dyspeptic editorial in the Des Moines Register last weekend urging the president to give up plans for reelection and to work full-time on national problems. The equally unexpected -- and undoubtedly unwelcome at the White House -- proposal by New York Gov. Hugh Carey that the president, along with Sen. Kennedy, release his delegates so that the convention can nominate some unidentified alternative was encouraged if not licensed by the president's public return to candidate status.

Jimmy Carter enjoyed his greatest political success in office not on the Delta Queen or after spending over-nights on some family's Castro convertible, but when he was president, in apparent charge of the Iranian hostage negotiations and strategy. If he were still in the exclusive role of commander-in-chief, he could have been at Tito's funeral in Belgrade yesterday and not at Temple University in Philadelphia today. Which appearance would have been more helpful to his reelection, to say nothing of the republic?

By virtually all counts, the race for the Democratic presidential nomination is over and Carter has won. If you are truly concerned about the reelection of Jimmy Carter and believe that it is in the national interest, why leave the White House and being president to become a candidate? And why now?