Architecture billings index steady in April-AIA

* Billings index down 0.9 pts to 42.8

* Project inquiries index rises to 56.8

* Architects still report 'difficult conditions'

NEW YORK, May 20 (Reuters) - A leading indicator of U.S. nonresidential construction activity held steady in April amid signs of renewed interest in construction projects, driven by U.S. stimulus funding, an architects' trade group said on Wednesday.

The Architecture Billings Index fell nine-tenths of a point to 42.8 last month after an eight-point jump in the prior month, according to the American Institute of Architects. The index has not crossed above 50 -- a level that indicates improving demand -- since January 2008.

All four U.S. geographic regions tracked by the group, and all four construction subsectors, remained below 50. However, a measure of inquiries for projects rose slightly to 56.8, reflecting builders' interest in stimulus-funded projects.

The data suggested demand may be returning over a period of several months, rather than pointing to a rapid recovery, the AIA said.

"Too many architects are continuing to report difficult conditions to feel confident that the economic landscape for the construction industry will improve very quickly," AIA Chief Economist Kermit Baker said.

The AIA's Billings Index, which began in 1995, is considered a measure of construction activity nine to 12 months in the future. Nonresidential construction includes commercial and industrial facilities such as hotels and office buildings, as well as institutions including schools and hospitals.

Companies that sell to this market include diversified manufacturer Honeywell International Inc (HON.N), lighting maker Acuity Brands Inc (AYI.N) and electrical components maker Thomas & Betts Corp TNB.N, as well as heating and cooling systems makers Ingersoll-Rand Co (IR.N) and Johnson Controls Inc (JCI.N).

Caterpillar Inc (CAT.N), Deere & Co (DE.N), Terex Corp (TEX.N), Illinois Tool Works Inc (ITW.N) and Eaton Corp (ETN.N) are also exposed to the sector. (Reporting by Nick Zieminski, editing by Maureen Bavdek)