SILVER SPRING, Maryland (Reuters) – Novartis AG failed to win support from a U.S. advisory panel for the highest proposed dose of a new lung drug, a setback that could delay development of a potential blockbuster medicine.

A Food and Drug Administration advisory panel voted 13-4 on Tuesday to urge approval of a lower dose of inhaled drug indacaterol for treating chronic obstructive pulmonary disease (COPD), the third leading killer of Americans.

But in a 12-5 vote, the panel declined to endorse the higher dose. Opponents said they were not convinced the higher dose provided any additional benefit.

"I saw no compelling evidence there was a significant difference" between the two doses, said Dr. Peter Terry, the panel chairman and a professor of medicine at Johns Hopkins in Baltimore.

The lower dose is 75 micrograms and the higher dose is 150 micrograms.

The FDA usually follows panel recommendations. a final decision on indacaterol is due by April 1.

Modest sales are forecast for indacaterol as a stand-alone treatment, but analysts say the drug could bring in more than $5 billion a year when combined with another lung therapy.

Novartis is seeking approval to sell indacaterol for COPD, also known as smoker's cough because smoking is the major cause. The disease causes breathing trouble and chronic coughing and is sometimes fatal. an estimated 80 million people worldwide have moderate to severe COPD, according to the World Health Organization.

Indacaterol is a once-a-day long-acting beta agonist, or LABA, a type of drug used to open to airways in patients with asthma or COPD. other LABAs are taken twice a day. The drugs carry strong warnings about worsening of asthma and deaths in some patients.

Novartis and GlaxoSmithKline Plc are racing to sell a two-in-one medicine that combines a LABA with long-acting muscarinic antagonist (LAMA) to produce a more effective, convenient therapy.

The Novartis combination product, known as QVA149, combines a LAMA with 150 micrograms of indacaterol. an FDA rejection or delay on that dose could stall the combination product, analysts said before the meeting.

Until recently, Novartis was not on the radar as a major force in lung drugs, which are difficult to make because of the inhaler devices they require for delivery.

Now the field is emerging as pivotal to the company's future through the drive into new branded drugs plus work with partner Vectura on generic copies of products like Glaxo's Advair and AstraZeneca's Symbicort.

Indacaterol already is sold as a single therapy in Europe under the brand name Onbrez Breezhaler and had revenues of $33 million in 2010. its U.S. name will be Arcapta Neohaler.

Novartis told the panel the higher dose provided better relief of COPD symptoms with no greater safety risk.

"Patients need a safe therapy that is optimal and not just minimally effective," David Morris, head of respiratory products for Novartis Pharma, told the panel.

Novartis shares fell 1.3 percent to close at $55.48 on the New York Stock Exchange.

(Reporting by Lisa Richwine; Editing by Tim Dobbyn)