The manifest danger Islamic radicalism presents to the United States ought to be unifying American politicians around programs to keep the country safe. But their behavior this summer shows they prefer petty partisanship.

A series of decisions Congress must make in September — particularly on measures to authorize the National Security Agency’s Terrorist Surveillance Program and military tribunals for terrorist detainees — will determine whether they can find a common purpose.

The two sides should be looking at each others’ agendas — the Democrats’ advocacy of homeland security upgrades and some conservative ideas on terrorist “profiling” — to improve security.

And both should seriously consider the prospect of creating a domestic security agency like Great Britain’s MI5, particularly given the FBI’s evident failure — as reported in The Washington Post this week — to adapt its criminal investigation culture to antiterrorist intelligence-gathering.

But, based on the record, the prospects for cooperative action are not good. The minute Britain announced the arrest of radicals planning to blow up U.S.-bound airliners over the Atlantic, Republicans and Democrats began squabbling over what it meant — especially for their November election prospects.

Senate Minority Leader Harry Reid, D-Nev., put out a press release declaring the plot “demonstrates the need for the Bush administration and the Congress to change course in Iraq and ensure that we’re taking all the steps necessary to protect Americans at home and across the world.”

Republican National Committee Chairman Ken Mehlman responded, “Instead of focusing on political attacks, we should focus on the fact that we are at war and need every tool to win the war on terror. If Harry Reid had his way and (had) killed the (USA) PATRIOT Act and ended the terrorist surveillance program, authorities would be less able to uncover terrorist plots.”

Had the terror plotters not been stopped, 10 or so 747s might have exploded in mid-air on Aug. 16, one reported target date, or yesterday, Aug. 22, a portentous date in the Islamic calendar. More people might have been killed than those who died in the Sept. 11, 2001, terrorist attacks.

If it had happened, would the catastrophe have roused American politicians to halt their nonstop partisan warfare in the realization that we are all in this together?

Five years ago, Sept. 11 brought Americans together, including Republicans and Democrats. But this year, the evidence dismally suggests, an 8/16 or 8/22 would have intensified the politicians’ finger-pointing.

The blame-casting hasn’t ceased despite a war in Lebanon in which the Islamist radical group Hezbollah was the perceived winner and as its sponsor, Iran, continued work on nuclear weapons. The danger to us all is mounting, but U.S. politicians are thinking primarily about making partisan points.

They were at it again when U.S. District Judge Anna Diggs Taylor issued a tendentious ruling striking down the NSA surveillance program and after President Bush made a fervent case that premature withdrawal from Iraq would be a moral and strategic “disaster.”

Democrats think they can gain the advantage by declaring Iraq a diversion from the “real” war on terror against Al Qaeda and the Taliban, which they say they’d fight aggressively in Afghanistan and with measures to protect U.S. ports, chemical plants and airplanes.

As Democratic National Committee Chairman Howard Dean put it, “We are bogged down, spending half a trillion dollars in Iraq, which could be used to do the things that the Democratic Party and the 9/11 Commission have recommended, which is to make our airports and our nuclear power plants and our train stations safe here at home.”

Reid, along with Democratic Sens. Carl Levin, Mich., and Jack Reed, R.I., held a telephonic press briefing Tuesday making similar points and issued a statement headlined “The Bush Record of Failure: Not Getting the Job Done in the War on Terror,” which chiefly protested the failure to capture Osama bin Laden.

Republicans think they gain by calling the Democrats “defeatists” on Iraq and by asserting that Democrats are “weak” on terror because they opposed the NSA wiretap program and had qualms about efforts to track terrorist finances through the international banking system.

Who’s actually gaining in this struggle is hard to tell. Traditionally, Republicans lead Democrats in public trust on fighting terrorism by margins of 25 to 30 points, but recent polls have shown that advantage dropping to single digits.

A Pew poll last week showed that more Americans, 69 percent, are concerned Republicans would get the United States involved in new wars than the 57 percent who are worried that Democrats are weak on fighting terror.

However, this week, a Gallup poll reported Bush’s overall approval rating rose to 42 percent from 37 percent over the two weeks since the London plot was stifled and, for his handling of terrorism, to 55 percent from 47 percent.

But for handling Iraq, he remained mired at 36 percent. And a CBS/New York Times poll showed Americans, by 51 percent to 32 percent, don’t think Iraq represents a “major part” of the war on terror.

If the election hinges on “terror,” Republicans may win. If it’s “Iraq” and things keep looking grim there, it’s a Democratic advantage. That will frame the argument through November.

But, meantime, the two sides should try to accomplish a few things. It was a good sign that Reid, along with even liberal firebrand Rep. John Conyers, D-Mich., responded to Taylor’s NSA ruling by saying they agreed terrorists should be wiretapped, even if they said Bush had started the warrantless program illegally.

Reid said in his telephone conference Tuesday that Democrats “stand ready to work with Republicans” on the NSA program and on authorizing military tribunals for terrorist captives following the Supreme Court’s ruling that Bush’s tribunal plan was unconstitutional.

The Senate Judiciary Committee is due to consider bills in September on both programs. They will test whether American politicians can respond to a common threat with common purpose. Our enemies are watching.

(Morton Kondracke is executive editor of Roll Call, the newspaper of Capitol Hill.)