Sept 24 (Reuters) - The Architecture Billings Index, an indicator of U.S. non-residential building activity, fell slightly in August, after hitting a seven-year high the previous month.

The ABI stood at 53.0 in August, down from 55.8 in July, the American Institute of Architects said on Wednesday.

The index, based on a survey of U.S. architects, reflects the roughly nine to 12 months between architecture billings and construction spending.

A reading above 50 indicates an increase in billings.

"Long awaited access to credit from lending institutions and an increasing comfort level in the overall economy has helped revitalize the commercial real estate sector in recent months," AIA chief economist Kermit Baker said in a statement.

Industrial companies and their investors track the monthly index as an indicator of future demand for machinery and components used to erect buildings.

The new projects inquiry index fell to 62.6 in August from 66.2 the previous month.

(Reporting by Mridhula Raghavan in Bangalore; Editing by Don Sebastian)