* Some 900 workers join 700 already on strike
* Union to consider widening strike to all its members
* Equinor sees no short-term impact on output (Adds union, Equinor comments, background)
OSLO, July 16 (Reuters) - Some 900 Norwegian offshore oil and gas workers went on strike on Monday, joining almost 700 who walked off the job last week, in an escalating dispute over pay and pensions that has hit production.
The Safe union said it would consider in the next few days whether to widen the strike to all its 2,250 members.
Safe went ahead with its plan to expand the strike that began last Tuesday after employers did not respond to its demands for higher wages and pension benefits by a midnight (2200 GMT) Sunday deadline.
It is the biggest strike in the sector since a 16-day industrial action in 2012 cut Norways output of crude by about 13 percent and its natural gas production by about 4 percent.
Reidun Ravndal, a member of Safe's strike committee, said 900 additional workers were joining the strike on Monday, although it would take some time for the strike to become fully effective because they have to follow safe shutdown procedures.
Asked whether the strike might be widened to the remaining drilling workers that belong to the union, Ravndal told Reuters: "we will have this discussion in the next few days."
The remaining employees work on rigs that drill production wells, not on platforms producing oil and gas, Safe said.
The oil and gas rig workers went on strike after rejecting a proposed wage and pension deal. There has been no contact between employers and the union since the strike began last Tuesday.
Employers, represented by the Norwegian Shipowners' Association, said on Monday that the union "lacked understanding of the economic reality of the Norwegian continental shelf."
"It is ... utterly incomprehensible that Safe is willing to put at risk jobs, the shelf's attractiveness and competitiveness, and Norway's reputation as a safe and stable supplier of oil and gas resources," lead negotiator Jacob Korsgaard said in a statement.
On Saturday, Korsgaard told Reuters the Shipowners' Association planned no compromise talks. "Obviously a conflict like this cannot go on forever. All counter-measures are considered," he said, without giving details.
The expanded strike is not expected to have any immediate extra impact on oil or gas production beyond the closure last week of Shell's Knarr field, which produces 23,900 barrels of oil equivalent per day.
Norway's Equinor does not expect its output to be affected "in the short term" due to the escalation of the strike, the firm said.
"More drilling and well operations are affected. We will get delays ... In the short-term we do not see any production or milestone consequences," said Equinor spokesman Eskil Eriksen.
He declined to comment on what the company considered "short-term" and what the long-term consequences would be.
Last week Aker BP said a prolonged strike could postpone output from some of the wells it was planning to drill at its Valhall field, which it expected to put in production later in the year.
Both the Safe union and employers said late on Sunday there had been no contacts or new offers during the weekend.
The employees joining the action work on exploration and production drilling rigs owned by Saipem, Transocean , Songa Offshore, Odfjell Drilling, Archer and COSL, among others.
Norway's oil sector directly employed 50,700 workers in 2017, of whom 26,700 worked in production and 23,500 in related services, according to Statistics Norway. The rest were occupied in transportation through pipelines. (Editing by Alister Doyle and Adrian Croft)