* Tens of thousands of workers stage strikes on Tuesday
* Further walkouts planned for Wednesday
* IG Metall demands 6 pct higher pay, right to shorter hours
* Labour leader says dispute may escalate over working hours (Adds number of workers on strike, companies affected, changes dateline)
By Maria Sheahan
FRANKFURT, Jan 9 (Reuters) - German industrial workers widened industrial action on Tuesday, with nearly 60,000 staff at 280 metals and engineering companies downing their tools in support of wage claims by union IG Metall.
With the economy in robust health and unemployment at record lows, the country's biggest union is demanding an inflation-busting 6 percent pay hike this year for about 3.9 million workers.
It is also making a push for shorter hours, more than two decades after it won the 35-hour work week for Germans.
Ahead of a round of regional negotiations due to begin on Thursday, employers have so far offered 2 percent plus a one-off 200 euro ($240) payment in the first quarter and rejected demands for shorter hours.
In the state of North Rhine-Westphalia alone, the industrial heartland of Germany, workers at 140 companies including Siemens and Thyssenkrupp staged walkouts and marched outside factory gates carrying banners.
In other parts of the country, companies including engineering group Siemens, carmaker BMW, automotive suppliers Schaeffler and farm equipment maker John Deere were affected.
Since the start of last week, a total of around 80,000 workers have taken action across the nation, including Tuesday's walkouts, the union said. IG Metall has announced further walkouts for Wednesday.
Such industrial action is common in Germany before sector-wide pay negotiations, and similar walkouts took place in 2016 and 2015.
The union has made it clear it is drawing a line in the sand regarding shorter working hours and has threatened to move beyond walkouts lasting only a few hours to all-out strikes across the sector.
The union has called for higher wages as well as a right to reduce weekly hours to 28 from 35 and return to full-time employment after two years for shift workers and those who need to care for children or elderly relatives.
Employers have so far rejected the demand because it includes a provision under which companies would help make up for the pay shortfall for some workers who shorten their hours.
Talks between unions and employers' associations are set for Thursday in the southwestern state of Baden-Wuerttemberg, where Volkswagen's Porsche, Mercedes-Benz maker Daimler and automotive suppliers including Bosch are based.
"If we do not see any willingness to even discuss the topic seriously on Thursday, the situation will escalate further," Roman Zitzelsberger, head of IG Metall in Baden-Wuerttemberg, told German daily Handelsblatt.
Next door in Bavaria negotiations will resume on Jan. 15, and to the north in North Rhine-Westphalia on Jan. 18.
The labour dispute follows a strong year of growth in Europe's largest economy, driven by domestic demand from record numbers of German workers while borrowing costs and inflation remain low and exporters benefit from a global recovery.
That pattern should extend through 2018, with the Ifo economic institute last month forecasting growth of 2.6 percent for the year. ($1 = 0.8299 euros) (Additional reporting by Jan Schwartz and Ilona Wissenbach; Editing by Alison Williams)