TOKYO, Dec 15 (Reuters) - Japan's Nikkei inched down ahead of a crucial policy decision by the U.S. Federal Reserve on Wednesday, with declines in shipping stocks outweighing gains in carmaker Toyota and its group companies.

The broad Topix index, however, posted a 0.37% gain at the midday break, with eight shares advancing for every five that sank. The Nikkei share average slipped 0.08%, giving up earlier gains.

Investors expect the U.S. Federal Open Market Committee (FOMC) to adopt a more hawkish tone at the conclusion of their two-day meeting, quickening the pace at which they taper bond-buying stimulus and potentially setting up earlier interest rate hikes.

"Position adjustments before the FOMC are center stage, and it's not possible to discern a direction to the market amid that," said Hajime Sakai, the chief fund manager at Mito Securities Co in Tokyo.

Toyota was the second-best performer among the 30 core Topix names, notching a 2.69% gain after Japan's biggest automaker said on Tuesday it would commit about $70 billion to electrify its lineup by 2030.

That also lifted its group companies, with Toyota Tsusho and Denso jumping 4.20% and 4.31%, respectively.

Transport equipment was the Topix's best performing sector, adding 1.99%.

Among other notable gainers, Recruit Holdings and SoftBank Group rose 2.97% and 2.14%, respectively, as they rebounded following recent slides. Sony advanced 1.93%.

At the other end, sea transport's 3.97% tumble made it the worst-performing Topix sector by a wide margin. (Reporting by Tokyo markets team; Editing by Devika Syamnath)