* Vinci H1 results, Aug 31 after close
* Average EBIT forecast 1.354 billion
* Average net attributable profit forecast 637 million
PARIS, Aug 28 (Reuters) - French public works group Vinci is set to report first-half earnings before interest and taxes down 5.3 percent, at 1.354 billion euros ($1.94 billion), an average of six analysts polled by Reuters showed.
The average net profit was seen down 12.9 percent, at 637 million euros, the poll showed, as the economic downturn is taking it toll on margins.
Last year, Vinci reported first-half EBIT of 1.43 billion euros, and a net income of 731 million euros.
The world's biggest construction and concession group is due to report its first-half 2009 earning results on August 31, after the market's close, followed with an analyst call on September 1 at 0630 GMT and a news conference at 0900 GMT.
Analysts said they would look for any indication on full-year 2009 objectives and a possible confirmation of a pickup in motorway traffic during the summer.
The impact of the different stimulus packages implemented in countries where Vinci operates is also expected, as it had not benefited the group's "contracting" division by the end of the second quarter.
Analysts said they would also focus on possible lower margins as the world economy remains weak, as well as the distribution of the group's sales in France and overseas.
Vinci secured a number of big contracts outside its domestic market in the first half of the year, including a 1.2 billion euro public-private partnership (PPP) road project in Slovakia, a 1 billion euro project for the Moscow-Saint Petersburg motorway, as well as 323 million euros for the Cairo metro.
The group last month reported sales down 3.2 percent, at 15.2 million euros, and maintained its objective announced last March of a stabilisation in revenue from French road concessions and a limited fall in revenue from "contracting" (Construction, Energy and Roads). (Reporting by Gilles Guillaume, Writing by Michel Rose; Editing by Rupert Winchester)