Washington ? It’s a rule of thumb in Middle East conflicts that whenever peace talks are announced, each side steps up the fighting so it can grab as much territory as possible before the cease-fire lines are drawn.

This struggle for position is happening now in Syria, in the run-up to planned negotiations in Geneva next month that will be co-sponsored by the United States and Russia. But the battling on the ground is so intense, and the demand for additional weapons so vocal, that a skeptical person should ask whether the Geneva talks will take place at all. The two sides may have to fight a while longer before they’re ready to talk.

It’s axiomatic that neither side wants to negotiate from weakness. For the regime of President Bashar al-Assad, that means more Russian weapons and an intense battle (backed by Hezbollah) to control the strategic city of Qusayr, near the Lebanese border, which links Damascus with Assad’s Alawite homeland in the northwest. Assad is also bargaining tough about the transition, claiming he wants to stay in power until the Syrian people vote in elections.

A good summary of the rebels’ conditions for Geneva came in a telephone interview Monday with Gen. Salim Idriss, the commander of the rebels’ Supreme Military Council. He spoke from Jordan, where his forces had just received a new shipment of 35 tons of weapons from Saudi Arabia; Idriss said these weapons will help, but they aren’t advanced enough to combat Assad’s tanks and planes fighting in Qusayr.

Idriss said he would not attend the Geneva talks unless the U.S. and its allies establish “military balance” by giving him modern anti-tank and anti-aircraft weapons. “It’s not valuable to go to negotiations when we are weak on the ground,” he said.

Rebel forces are chronically short of ammunition, Idriss said. According to one rebel source, he has privately asked the U.S. for 700 tons of ammunition each week over the next month to help strengthen the rebels’ hand and provide leverage before Geneva.

The rebel commander said that Assad is “preparing to bring regime representatives to Geneva in a very strong position. They are trying to tell us that we are weak and we are not unified, and we have to accept everything they say.” Even if Idriss doesn’t get more weapons from the West, he said he is “prepared to fight for 100 years” to topple the regime.

Rebels sources told me that Idriss believes it would be “suicidal” for any opposition leader to go to Geneva without a “green light” that Assad and his inner circle will be removed during the transition.

Idriss sent a letter to Secretary of State John Kerry last weekend summarizing these pre-negotiating positions. He said the “pressing objective” now is to stop the killing and prevent “total state collapse.” He said his forces “would welcome a peaceful transition” to a new “interim authority” that would include both the opposition and “government members of the departing regime who did not order or participate in atrocities.”

“For the negotiations to be of any substance, we must reach a strategic military balance, without which the regime will feel empowered to dictate, or at least stall for precious time,” Idriss wrote to Kerry. He called for reform of the army but dissolution of the security services that have run Assad’s police-state regime.

During the interview, Idriss said he hoped to open channels to Russia before the Geneva talks. He’s ready to meet Russian Deputy Foreign Minister Mikhail Bogdanov to discuss Russia’s future role in Syria, and that he would bring along three other rebel commanders.  

Idriss also tried to address White House fears that modern anti-aircraft weapons given to the rebels might fall into the hands of extremist groups. He said the advanced weapons would be controlled by trained fighters who had Syrian army experience, and that trusted contractors could transport them and make sure they were secure.

The power of extremists within the opposition is sadly demonstrated by the situation in northeastern Syria. The al-Nusra Front, an offshoot of al-Qaida, is said to be especially powerful in the Deir El-Zour region, controlling local cotton sales, distributing 100 captured vehicles to fighters and planning to market the region’s oil. An opposition source described the situation there as “very worrisome.”

Here’s Idriss’ biggest test. He must speak the language of diplomacy, but he must also show his strength as a military commander — and not just battling Assad in the west, but combating extremists and warlords in the north and east.