Trade and Foreign Ministers meet ahead of the Apec leaders summit at the weekend, which Prime Minister John Key is having to skip for the election campaign.
Mr Groser said he expected there would be"a partial agreement" at Hawaii.
Negotiators so far had tackled only the "low-hanging fruit."
"We haven't got down to the tough stuff," he said, such as agriculture access and intellectual property.
"We're going to get some tough asks on IP - I understand that but we're up for that," he said.
But cognisant of the difficult political management issues for the United States and a presidential election next year, Mr Groser has issued an invitation to US counterpart Ron Kirk to start the hard issues whenever the US deems it is ready to do so.
The negotiation was "not that hard" for Australia and New Zealand because they had no deeply protected sectors any more.
But the United States faced tough political management problems. However Mr Groser did not necessarily accept the conventional wisdom that the United States would put off the hard part of TPP negotiations next year because of the presidential election.
"It may well be that the Americans want to demonstrate in difficult economic times that the United States is capable of taking some tough decisions. I can't call it."
Mr Groser there had been no political negotiating so far on the agreement and the discussion at Apec would be a"political positioning."
He thought it would be a "very intriguing meeting" not least of which was because of what was happening in the Eurozone.
President Obama and several other Apec leaders would be coming from the G20 meeting in Cannes and that would still be fresh in their minds.