SAN FRANCISCO: Twitter chief executive Evan Williams has spoken optimistically about the popular microblogging service's future despite slowing US growth and no clear plan for making money.

"The number of interesting things we can do with Twitter is just endless," Williams said during an on-stage chat with John Battelle on the opening day of a Web 2.0 Summit in San Francisco. "It just blows my mind."

Williams was upbeat during the talk, saying that while use of Twitter's website is slowing in the United States it is gaining big internationally and with smart phone users.

"Our US Twitter.com growth has slowed temporarily and there are some things we will be launching that we think will pick that back up," Williams said.

Williams sidestepped questions about Twitter's plans for cashing in on its popularity, saying the San Francisco-based company's priority is to improve its technology and reliability.

"It's not like we are spending our days looking under couch cushions for the elusive revenue model," Williams said. "Obviously, we are thinking about it."

Restaurants use Twitter to fill empty tables. Masseuses use Twitter to fill empty slots between appointments. Shops use Twitter to sell overstocked merchandise. Food carts use Twitter to guide customers to street corners.

"That is all happening today," Evans said. "If we are driving that value for businesses, I am not worried about us driving some of that value for ourselves."

Williams said it would be a mistake to get distracted from improving Twitter's ability to deliver the "freshest and most relevant" information because that will be a key to Twitter making money.

Twitter is considering hiring a sales force and is considering making money from advertising, according to the chief executive.

There are a large number of companies interested in working with Twitter to promote brands, according to Williams.

"We are optimistic about revenue," Williams said. "I can't tell you want the mode is."

Twitter is working on making it easier for newcomers to the microblogging service to immerse themselves in a world of followers, following, and expressing thoughts in text messages of no more than 140 characters.

Twitter's top five growth areas are Britain, Brazil, Indonesia, Japan and the United States. Launches of mobile Twitter services in India and Japan last week are expected to cause use in those countries to surge.

"I'm not as concerned as I used to be about Twitter's ability to scale," Williams said.

Twitter has released a test, or beta, version of a Lists feature for organizing microblogging feeds and is building search tools so users can more easily sift torrents of commentary for tidbits of interest.

"We're putting a ton of effort into search and discovery on Twitter," Williams said.

"We have millions of nodes collecting information but we need to get much more intelligent in how we search that."

Twitter is also crafting rules for the outside developer that craft programs for users of the microblogging service.

"We need to get a lot better about assuring developers they can invest in our platform," Williams said.

Improved relations with developers and enhanced search tools can be woven into ways to make money from Twitter services or features.

Williams said that Twitter's battle against spam resulted in some "overactive spam-killing scripts," or automated programs, suspending accounts of non-offenders and "in those cases it was our screw-up and we apologize."

Williams said he had no regrets about rejecting an offer by Facebook to buy Twitter in a 500-million-dollar stock deal.

"I just didn't see a reason to sell," Williams said. "Because that is not the point. The point is to see what we can build. We believe Twitter with an open exchange of information is a good thing for the world."

Twitter's goal has never been to attract a hefty offer and then cash out, according to Williams.

"We think of Twitter as not a social network but an information network," Williams said.

Williams said he admires Facebook's agility when it comes to adapting its features and offerings but that Twitter isn't cowering before the might of the social-networking powerhouse.

"I'm pretty sure the world is big enough for Facebook and Twitter," Williams said. "I think they are good for different things. I'm pretty sure the open exchange of information will prevail in the end."