Republicans questioned Thurs­day why the Federal Communications Commission fast-tracked an initial approval for a company — well-connected among Democrats — to provide cellphone service through satellites, a technology that other agencies say disrupts Global Positioning System devices, hurricane-tracking systems, and military and commercial airlines.

The FCC gave a crucial green light for Reston-based LightSquared in January without a full commission vote, despite warnings from companies and federal agencies that the satellite network would harm communication systems crucial to national security and public safety, GOP lawmakers said.

But the FCC has defended its process, saying it has led to better understanding of a promising technology.

At a House hearing Thursday, Republicans criticized the FCC for not using its own engineers to examine whether LightSquared’s technology posed interference issues. The agency relied on tests run by the company and the GPS industry.

Separately, in a letter, Sen. Charles E. Grassley (R-Iowa) said the FCC has refused to answer his questions or hand over e-mails and other correspondence between LightSquared and the agency.

“Persistent stonewalling only raises more questions and heightens suspicion regarding the FCC’s actions,” Grassley, the ranking Republican on the Judiciary Committee, said in a statement. “Without transparency, and with media coverage of political connections in this case, there’s no way to know whether the agency is trying to help friends in need or really looking out for the public’s interest.”

The FCC has told Grassley his committee does not oversee the agency and such requests should come from the appropriate lawmakers on the House Energy and Commerce Committee, which has yet to look into the matter.

An FCC spokeswoman added that the agency granted expedited approval for plans in January only on the condition that the company resolve interference problems with GPS providers and other technologies.

“The process we set up has been tremendously successful, yielding a deeper understanding of the issues by both LightSquared and the GPS industry,” said Tammy Sun, an FCC spokeswoman.

Responding to criticism that the agency didn’t use its own engineers to test for interference, an FCC official said the agency believes that “companies are in the best position to understand their own technologies.” The official spoke on condition of anonymity because the FCC process is ongoing.

Agency officials, including Chairman Julius Genachowski, have touted the ambitions of LightSquared, a $14 billion venture financed by billionaire Philip Falcone, saying the company will create thousands of jobs as it erects cell towers and brings cellular and high-speed Internet service to remote areas. The venture also seemed to support the Obama administration’s goals to spread mobile broadband service to more Americans.

While the FCC considered LightSquared’s plans, Falcone donated huge sums to the Democratic Party and met with White House officials — facts reported in July by the Center for Public Integrity’s iWatch News.

When asked whether the White House influenced the FCC on LightSquared’s waiver, White House spokesman Eric Schultz said: “The Federal Communications Commission is an independent agency with its own standards and procedures for considering these types of decisions, and we respect that process.”

Within the FCC, a senior official said the chairman’s office didn’t seek enough input from the agency’s five-member commission when it moved forward in January on the conditional approval for LightSquared.

The approval was “a fait accompli,” said the official, who spoke on condition of anonymity because the person was not authorized to speak publicly.

Officials from other agencies have said LightSquared’s technology, if allowed to become fully operational, would pose grave problems.

The Federal Aviation Administration said LightSquared’s plan would cost billions of dollars to retool navigation systems — and could even lead to the deaths of as many as 800 people over a decade through airplane accidents, according to an internal FAA report.

The Defense Department said the precision of its drones and other technology would be harmed by devices on LightSquared’s network that would crowd out signals for the military’s GPS technologies.

The satellite network could also disrupt hurricane tracking, according to industry officials and GOP lawmakers who held a Science, Space and Technology Committee hearing on LightSquared on Thursday.

Committee Chairman Ralph M. Hall (R-Tex.) wanted to know the FCC’s next steps.

“Although the FCC has stated it will not allow LightSquared to begin commercial service without first resolving the interference issue, nothing actually prevents the FCC from moving forward at this point,” he said.

Democrats at the hearing noted that nothing has been finalized and expressed confidence that the FCC would ultimately consider all the facts before the satellite system is fully launched. Ranking Democrat Eddie Bernice Johnson (Tex.) said: “The LightSquared proposal to build a nationwide broadband network in the frequencies that sit next to GPS has provoked enormous controversy. However, I do not believe that the FCC would make a decision that compromises GPS services.”

But GOP lawmakers and members of a coalition formed by the GPS industry also noted that the spectrum used by LightSquared was never intended for cellphones. The FCC in 2002 granted a licence to LightSquared, then known as SkyTerra, on the condition that its primary business would be to provide services for satellite phones.

This is a case where “sufficient homework was not done” by the FCC, Scott Pace, director of the Space Policy Institute at George Washington University, said at the hearing.