* Sees 2012 operating profit flat on higher vehicle sales
* To reach sales target of 1.5 mln cars earlier than planned
* CFO says realistic medium-term margin is 8-10 pct
* 2011 operating margin 12.1 pct vs 9.4 pct yr-ago
* More than 90 pct of Volkswagen's net cash comes from Audi (Adds CEO comments from interview, Lamborghini)
By Irene Preisinger and Jamie McGeever
INGOLSTADT, Germany, March 1 (Reuters) - Audi is scaling back ambitions to maintain record profit margins this year in the face of ramp-up costs for its new compact car, higher spending on research and development and investments to expand in China.
Echoing similar downbeat comments from rival Mercedes-Benz last month, Volkswagen's premium brand said on Thursday that a likely 4 percent-plus increase in car sales this year might not translate into an earnings improvement.
Speaking to Reuters Insider, Chief Executive Rupert Stadler said Audi might be able to revisit its guidance later in the year when it knows "how the business is really going on in terms of growth rates."
Audi's operating margin widened by nearly three full percentage points to 12.1 percent last year, far above the 9.0 percent achieved by rival Mercedes.
Asked if he expected Audi to maintain last year's level of profitability, Stadler said: "This should be our target of course."
However Audi finance chief Axel Strotbek earlier told a news conference the carmaker was sticking to its mid-term sustainable target of 8-10 percent.
Operating profit jumped 60 percent to a record 5.35 billion euros ($7.16 billion) last year on the back of surging sales to China, its largest market, where Audi sells one out of every four cars.
Audi overtook Mercedes last year as the world's second- largest premium carmaker and is now in a close race with the BMW brand for the top spot.
"Never have our vehicle sales to retail customers increased as much in a single year," Stadler told reporters, after sales volume jumped by almost a fifth to 1.3 million cars.
The Ingolstadt-based carmaker said it now wants to meet its 2015 target of selling 1.5 million vehicles in 2014 at the latest.
Audi's net cash rose to over 15.7 billion euros at the end of last year, meaning more than 9 out of every 10 euros in Volkswagen's war chest came from its premium brand.
Shares in Volkswagen rose by 2.4 percent by 1537 GMT, outpacing a 1.4 percent increase in the European auto sector index.
Separately, Audi's exotic Italian sports car brand Lamborghini reported revenue growth failed to keep pace with vehicle sales, rising 19 percent to 322 million euros last year.
The manufacturer of the Reventon limited edition sports car, which was sold out at a price of about 1 million euros before it was ever made, expected to increase sales this year after delivering 1,600 cars to customers worldwide in 2011. ($1 = 0.7476 euros) (Reporting by Irene Preisinger; Writing by Christiaan Hetzner; Editing by David Cowell)