* 17,000 initially affected; could increase to over 170,000
* Workers demand biggest rise to worst paid
* Strikes have become common as Norway outperforms Europe (Adds detail)
OSLO, April 3 Around 17,000 Norwegian private sector workers could walk off the job on Monday if wage negotiations fail and their numbers could eventually rise to over 170,000, shutting vital industries, unions said.
The strike could affect oil services firms, Oslo's Gardermoen airport and key manufacturers but will not affect firms in oil production, Norway's lifeblood, the LO and YS unions said in separate statements on Wednesday.
Strikes have become common in Norway over the past year as workers are demanding a greater share of the country's rare economic success.
The economy grew by 3.5 percent last year, even as the euro zone sunk back into recession, as Norway's vast oil wealth and stable state finances drive growth.
Workers from public employees to oil workers went on several strikes last year, forcing the government to intervene.
Norwegian workers make about 60 percent more than the European average and workers on average earned 39,600 crowns ($6,800) a month in 2012, Statistics Norway said earlier.
Employees in the vast oil sector, which accounts for over a fifth of the country's $500 billion GDP, earn over twice that figure, once lucrative overtime is added in.
Escalating the strike from the initial 17,000 will be at discretion of the unions, but they have to give four days of notice before additional workers can go off the job.
Norway's overall workforce is 2.7 million strong with private sector workers numbering around 1.9 million.
Unions have not publicly specified their wage demands but said they want the lowest paid workers to get the biggest increases to narrow the gap to top earners.
Negotiations broke down late last month and the sides have now turned to a government mediator, setting midnight on Sunday as the deadline for a deal.
Wages grew by around 4 percent last year, even as productivity stagnated, and the central bank expects wage growth of 4 percent or more in each of the next four years.
Firms potentially affected next week could include oil services firm Aker Solutions and fertilizer maker Yara while a threat to halt refuelling at Oslo's Gardermoen airport could affect firms like SAS and Norwegian Air Shuttle.
($1 = 5.8099 Norwegian krones) (Reporting by Balazs Koranyi and Terje Solsvik; editing by Ron Askew)