Washington ? The American and British governments are planning a joint training exercise to respond to a major, coordinated terrorist attack on both countries. “This will not be a desktop exercise,” says Britain’s Home Secretary David Blunkett, “but an actual test of our readiness to deal with a joint attack.”

The tough, plainspoken Labor Party politician who directs Britain’s police and counterterrorist forces is routinely explaining why he is in Washington this week. But what he says next — when I ask about the timetable for this major undertaking — is both revealing and unsettling.

The joint exercise, which will build on mock attacks staged in Britain last autumn, is unlikely to occur before the U.S. presidential election in November. But it also needs to take place before next spring, the home secretary adds, since that is when a window opens for Britain’s next general election.

At one level, Blunkett is merely reminding me of something no practical politician ever forgets: the political calendar in an election year will determine the timing and shape of other events that can be planned, managed or moved.

But Blunkett’s explanation also offers a glimpse of one of the most difficult tasks politicians face in this particular campaign season. They will constantly have to balance fear and reassurance on a campaign trail that stretches into a troubling new era.

Voters in the United States will elect a president for the first time in the continuing psychological shadow of 9-11. Candidates must sound neither alarmist nor complacent about the terrorist threat.

Trying to stage a national civil defense exercise in the run-up to an election “would be very difficult,” given the current corrosive political moods in both countries, Blunkett says. The incumbents would risk being accused of playing politics with national security.

“Politics and the people who comment on politics are now much more cynical than they used to be,” he adds. “They would use your grandmother’s birthday against you if they could.”

But that seems to me to be only part of the answer. Politicians on both sides of the Atlantic, and both sides of the aisle in each country, need to decipher and respond to the innate awareness of electorates that they live under new threats that are difficult to quantify, to respond to and at times even to imagine.

It is perhaps simpler to reduce discussions of the politics of 9-11 to a tactical level. Thus, George W. Bush and John Kerry argue over Bush’s initial campaign ad, which does not mention that epoch-altering day of horror but visually exploits it. Kerry’s campaign in turn sought to make hay from the exploitation.

The campaign debate must quickly rise above that level and address how an open society can protect itself “even when so many comforts seem unaffected, and the threat so far off, if not illusory,” in the words of Blunkett’s boss, Prime Minister Tony Blair.

The phrase comes from a remarkable speech Blair gave on March 5 in his home district of Sedgefield. Not surprisingly, Blair, who is under unrelenting attack for allegedly lying about or distorting the reasons for going to war in Iraq, sounded defensive in the talk.

But he also probed the uncertainty that pervades the beginning of a new century. For Blair, Sept. 11 “altered crucially the balance of risk” in the world. It “was a declaration of war by religious fanatics who were prepared to wage war without limit” at a time when weapons of mass destruction would give them the potential to do just that.

This horrifying new reality is difficult for societies to absorb. Blair went on to argue that the psychological dislocation “is partly why the conspiracy theories or claims of deceit have such purchase” in the United States and Britain, and elsewhere for that matter. “How much simpler to debate those than to analyze and resolve the conundrum of our world’s present state.”

The speech should be required reading, and emulation, for candidates for national office here this year. This is no time to substitute arguments over campaign ads or political tactics for the needed discussion of America’s role in a rapidly changing and more threatening world. Blair’s speech points the way to such a discussion.

One way to bring that about may well be to do the opposite of what Bush and Blair seem to have decided. Organizing a joint security exercise before November would focus Americans on the stakes involved in an election that does truly count.

• Correction: The Russian presidential election law, which is not part of the Constitution as I stated in my last column, sets terms under which elections and candidacies can be nullified. Moreover those terms are more complex than I indicated. Apologies and thanks to alert reader Robert Otto.

Jim Hoagland is a columnist for Washington Post Writers Group.