By Tim Hepher

PARIS (Reuters) - Europe's Airbus (AIR.PA) has lifted a stumbling block to delivery of the world's largest jetliner to Qatar but faces the growing prospect of delays for the first flight of its newest small jet, the A320neo, several people familiar with the matter said.

After a three-month dispute that had blocked the delivery of the first of ten A380 superjumbos ordered by Qatar Airways, the Gulf airline has agreed to take the new jet, they said.

Airbus declined to comment.

Qatar Airways, which had refused to take delivery of the first three aircraft, citing concerns about the quality of the cabin interior, was not available for comment. In July, its chief executive said he would seek compensation for the delay.

Separately, industry sources said Airbus had been forced to hold off the first flight of the A320neo because of what one described as a "minor" technical issue.

A spokesman for Airbus declined to comment on whether there had been a delay, but said the company's plan to fly the plane in the third quarter remained unchanged.

"Airbus and Pratt & Whitney are working together towards the first flight, and there is no change in plans to carry it out in the third quarter," the Airbus spokesman said.

However, a person familiar with the matter said it now looked increasingly likely that the first flight would be pushed back to the fourth quarter.

"When flight testing starts is less important than having a successful flight test campaign," the person said.

The A320neo, a revamped version of its best-selling A320 short- and medium-haul jet, is hugely important to Airbus after it sold more than 3,000, resulting in sharp increases in its share price. The airplane is due to enter service in 2015.

Airbus has not published a schedule, making it difficult to verify whether the timing has slipped within the official window. But the sources said the first flight had at one point been penciled in for the first half of September.

ENGINE SCRUTINY

Airbus plans a complex year-long flight test program using eight aircraft spanning three versions of the A320neo family. Each version has a choice of two types of engine, so the planemaker must achieve safety certification for six types.

The amount of testing and data storage and analysis needed to certify modern aircraft has soared, from 12,000 parameters when the current version of A320 made its debut in 1987 to 670,000 parameters for the A350, which is nearing certification.

Most attention is on the performance of the engines after problems with a broadly similar Pratt & Whitney engine caused the temporary suspension of flight trials for the Bombardier (BBDb.TO) CSeries, a new competitor to Airbus and Boeing jets.