PARIS — Europe’s Galileo satellite navigation system has fallen further behind schedule, with a September-October launch of the first two full-operational-capability satellites now scrapped in hopes the satellites can be ready for a December slot that may also be out of reach, according to industry officials.

The delay of the launch is having a domino effect on the program by delaying the order of the four to eight satellites necessary to complete the 30-satellite constellation.

The 28-nation European Union, which owns Galileo, is hesitant to commit to more satellites before seeing how the initial spacecraft in what is called Galileo’s Full Operational Capability (FOC) perform in orbit, officials said.

The two satellites are to be launched aboard a single Europeanized Soyuz rocket following exhaustive testing by the European Space Agency (ESA). They are the first of 22 FOC satellites built by OHB AG of Bremen, Germany, with payload units provided by Surrey Satellite Technology Ltd. of Britain.

The first of the two arrived in mid-May at ESA’s European Space Research and Technology Centre (ESTEC) in Noordwijk, Netherlands. But it has not yet begun the key thermal-vacuum testing, leaving too many unknowns for Galileo backers to commit to a December launch.

How the satellite performs during these tests, which will last several weeks starting in mid-August, will determine whether the launch slips into 2014, officials said. ESA is managing the testing on behalf of the European Commission, the executive arm of the European Union.

The second satellite remains at prime contractor OHB, where it is undergoing modifications as issues are discovered on the satellite at ESA’s premises. This satellite nonetheless will be shipped to ESTEC for testing before being cleared for launch.

For now, industry officials are setting aside issues related to the availability of the Europeanized Soyuz rocket, operated from Europe’s Guiana Space Center spaceport on the northeast coast of South America. But these issues also pose problems for a late-2013 Galileo launch.

Arianespace, the Evry, France-based launch consortium that operates Soyuz and the two other vehicles based at the French Guiana site, the heavy-lift Ariane 5 and the light-class Vega vehicle, is juggling a complicated manifest. Because it cannot find a proper pairing of satellites for a fall launch, Arianespace has scheduled no Ariane 5 flights between August and November. The year’s final flight has been pushed to December.

The deployment of launch teams and rocket-tracking radars at the Guiana spaceport means it takes two or three weeks to transition from an Ariane 5 to a Soyuz, or vice versa.

Arianespace’s 2014 manifest is crowded, with multiple Soyuz launches for Galileo planned to permit partial service introduction that year — a high priority at the European Commission. Arianespace has further said it may try to fit one or two more Ariane 5 launches into the 2014 manifest if pent-up commercial demand justifies it.

The Galileo program is under political pressure from the European Commission to launch at least once in 2013 — originally, two launches were planned — and above all to conduct enough launches by late 2014 to permit the commission to declare Galileo ready for use by then.

In a July 24 statement on Galileo’s progress, the commission listed just about every detail of the program’s status and cost except one: the launch schedule for the 22 FOC satellites.

The statement nonetheless said that Galileo’s open positioning, navigation and timing service — the one that most closely resembles the GPS signal available today — will be ready for “early services” in 2014.

The commission said Galileo’s Public Regulated Service (PRS), whose GPS equivalent is the military code, will be ready in “pilot phase” in 2014 as well.

Galileo’s Commercial Service — there is no GPS equivalent — will be ready for “proof of concept in 2014, with early service expected to start in 2016,” the commission said.

European Commission Vice President Antonio Tajani, who is overseeing Galileo, has said he will show no mercy to companies that do not meet their contracted delivery schedules.

Officials said Tajani is ready to make an example of the OHB team, which includes Surrey Satellite Technology Ltd. of Britain as Galileo FOC payload provider, by imposing financial penalties that industry officials said could be equivalent to 3 percent of the industrial contract. OHB’s two contracts with the commission for Galileo satellite production total around 800 million euros ($1.06 billion).

OHB Chief Executive Marco R. Fuchs declined to speculate on contract penalties but conceded in a July 25 interview that OHB had fallen behind the initial delivery schedule.

Fuchs said the reasons for the schedule slips are multiple, that the program is basically on solid ground and that the first FOC satellite has passed its functional testing.

ESA officials did not return requests for comment on the Galileo test results.

Industry officials asked about Galileo gave a variety of assessments as to how the testing at ESTEC has been progressing. They spoke of payload filters that caused delays, of thermal stability issues and problems related to the higher power that the FOC satellites should deliver relative to the four in-orbit Galileo validation satellites that were launched in 2011 and 2012.

European officials have said they need higher power to overcome potential signal overlaps with China’s Beidou navigation constellation. The overlaps would not cause interference with the Galileo signals, but would make it difficult to jam the Chinese signals without also jamming Europe’s own PRS.

Peter B. de Selding was the Paris bureau chief for SpaceNews.