The United States and Britain are lining up their naval forces for a possible attack on Syria. France is right behind them. All three countries are reacting to mounting evidence that chemical gas was used against Syrian civilians, leaving hundreds dead and injured.

Should the UN experts who are now investigating the incident confirm any involvement by the Syrian regime, a redline will have been crossed. The Obama administration has warned President Bashar al-Assad several times that the use of chemical weapons will lead to a military response.

With President Vladimir Putin remaining opposed to military intervention, the United States, Britain, and France seem determined to bypass the UN Security Council and establish their own coalition of the willing in order to launch military strikes against Syria.

Where does this put Angela Merkel, the German chancellor, in the middle of an election campaign? The German public, even though it is horrified by the use of chemical weapons in Syria, has no appetite for any military intervention. In a poll commissioned by the magazine Stern, 69 percent said they opposed a strike against Syria.

If Merkel decides in favor of supporting the intervention, the German electorate is likely to punish her on September 22. But if she decides against joining this coalition of Western forces, Germany’s reputation with its Western allies will be ruined. Such disunity will further weaken NATO and Europe’s defense ambitions.

In other words: Merkel is damned if she does and damned if she doesn’t.

Merkel did enough damage to Germany’s reputation in NATO when Berlin abstained from the UN vote to impose a no-fly zone over Libya in March 2011.

Germany later tried to mend fences with NATO and the United States by agreeing to send Patriot missiles to Turkey as a defensive measure against any attack by Syria.

At the time, the risks of a Syrian attack seemed small. That might now change, should NATO countries bomb Syria and should President Assad decide to retaliate. In that case, it would be hard to see German soldiers not becoming involved in the military campaign. Yet that eventuality does not get discussed in Berlin.

Of course, Western governments are not yet sure whether President Assad himself ordered the chemicals weapons attack or whether renegade groups inside the military or even rebel forces put them to use.

But the time is drawing near when the Obama administration and its NATO allies have to honor the redline they set since the outset of the Syrian war: to act if chemical weapons are used. It’s a question of credibility.

How the West deals with Syria’s use of chemical weapons is important for Israel, too. Any Israeli government is haunted by the idea of a chemical or nuclear attack by Iran, a country supporting the Assad regime.

Even more than any of her predecessors, Chancellor Merkel has emphasized Germany’s responsibility vis-à-vis Israel, guaranteeing its security. But how much would that promise be worth if Merkel was to stay on the sidelines now?

All the others major German parties — with the exception of the post-communist Left, which opposes any kind of military force — are torn between a reluctance to become engaged militarily and their commitment to the international community’s responsibility to protect.

The opposition Social Democrats and Greens loathe the idea of getting involved in another war, fearing an electoral backlash. Both parties’ grass roots are deeply pacifist.

Social Democrat Peer Steinbrueck, who is standing against Merkel, this week advised against rushing into a military intervention. There was, he said, too much confusion on the ground in Syria.

Claudia Roth, a leader of the Greens, said she had “extreme doubts that a military intervention will stop the conflict or de-escalate it.”

Yet during the Libya war, these two parties supported the principle of the responsibility to protect. They were highly critical of the German abstention at the UN.

Merkel’s coalition is just as ambiguous. The Free Democrats, her junior coalition partner, are highly skeptical of military intervention. They were the driving force behind Germany’s abstention over Libya.

But now, Guido Westerwelle, the Free Democrats’ foreign minister, said that should the use of such weapons be confirmed, “the world community must act. At that time, Germany will belong to those who support consequences,” he said.

In a similar tone, Merkel, through her government spokesman Steffen Seibert, said this past Monday: “The alleged widespread use of gas has broken a taboo.” Seibert did not explain, however, what consequences the German government would draw from such a breaking of a taboo.

It’s a fine line that Merkel will have to walk. She has to try to find a way to morally support a military intervention without actually participating in it. At the same time, she will have to avoid seeming inconsistent.

Such a position will be a hard sell to NATO, the EU, and Washington. As a security and strategic partner, Germany is becoming increasingly irrelevant, with devastating implications for Europe’s defense ambitions.