(Adds comments by Canada's chief negotiator, Canadian trade minister)
OTTAWA, March 28 (Reuters) - U.S. Trade Representative Robert Lighthizer on Wednesday expressed optimism that talks to modify NAFTA could be wrapped up quickly, but a top Canadian official was more downbeat, saying much work remained.
The United States wants to speed up the slow pace of negotiations on the $1.2 trillion North American Free Trade Agreement, citing a need to finish before a July 1 presidential election in Mexico.
"I'd say I'm hopeful -- I think we are making progress. I think that all three parties want to move forward, we have a short window, because of elections and things beyond our control," Lighthizer told CNBC television.
"But if there's a real effort made to try to close out and to compromise and do some of the things we all know we should do, ... I'm optimistic that we can get something done in principle in the next little bit."
Chief Canadian negotiator Steve Verheul, though, said, "We've got quite a bit of work do yet," and noted in speaking to reporters that Washington had not yet explained what it meant by an agreement in principle.
Officials from the three countries are supposed to meet in the United States next month for the eighth round of talks, although Washington has not announced dates yet.
Only six of the roughly 30 chapters have been closed and wide differences remain on sensitive topics such as dispute resolution and how much North American content should be contained in autos produced in the three NAFTA nations.
"There are obviously some significant gaps on many issues," Verheul said, citing the U.S. positions on dispute settlement, government procurement and a sunset clause that would allow one party to quit the pact after five years.
"Right now we are still quite a distance away from any kind of agreement on the approach to autos," he said.
Canadian Trade Minister Francois-Philippe Champagne said he was cautiously optimistic while noting a new pact would be in effect for decades.
"What we want is a good deal, not just any deal. You know, it's not about next Friday or next month," he told reporters.
Canadian Prime Minister Justin Trudeau last week said a deal was likely while stressing the challenges posed by the Mexican vote and U.S. congressional elections in November.
Trudeau spoke to U.S. President Donald Trump on Monday and "underscored Canada's commitment to conclude a modern, mutually beneficial NAFTA as soon as possible," Canadian officials said. (Additional reporting by David Lawder in Washington; Editing by David Gregorio and Leslie Adler)