Still, courts generally give federal agencies wide leeway to interpret the law, Mr. Ku said. “There’s usually a tremendous amount of deference.”

Huawei filed its petition for review in the United States Court of Appeals for the Fifth Circuit, which covers the region that includes Huawei’s American headquarters in Plano, Texas. The company asked the court to hold the F.C.C.’s order unlawful because the commission did not offer it due process protections before designating it a security threat.

“Carriers across rural America — in small towns in Montana, Kentucky, and farmers in Wyoming — they choose to work with Huawei because they respect the quality and integrity of our equipment,” Mr. Song said.

Huawei is embarking upon this new legal battle as the company’s fortunes, despite the onslaught from Washington and apprehension in other world capitals, appear to be looking up.

The Commerce Department has begun allowing some American suppliers to resume selling parts and other technology to Huawei. Earlier this year the department had barred such sales without prior approval. Huawei’s business has remained steady over all, thanks to brisk sales of its smartphones and telecom equipment in China.

Throughout the rest of the world, the company has been supercharging its efforts to court the sympathies of the public and of governments. Hundreds of journalists have been invited to visit Huawei’s campuses. The company’s founder and chief executive, Ren Zhengfei, has given interview after interview in which he assures the world that neither he nor his firm has anything to hide.

In Washington, Huawei has spent $1.9 million on lobbying this year, according to federal disclosures, dwarfing its past totals.