Gatland’s men are currently undertaking a gruelling fitness camp in the Swiss Alps ahead of the tournament in Japan.
Warm-up matches home and away to England and Ireland are to come before the team heads for the Far East and Williams is excited about what is to come.
“I’m looking forward to the World Cup and I’m feeling optimistic. Wales will be more than competitive in Japan and we should have the ability to top the pool,” he said.
“I do worry about the Australia game and Fiji too, but we should still get through.
“Wales do have decent strength in depth. New Zealand are the best team in the tournament, but Wales are there or thereabouts behind them.”
Wales claimed Six Nations and Triple Crown glory in March and Gatland’s side are ranked second in World Rugby’s rankings following a run of successive victories that currently stands at 14.
It is the best sequence of results in Welsh rugby history.
Wales face England at Twickenham on August 11 and then host Eddie Jones’ side at what will be a sold-out Principality Stadium the following Saturday.
After that they will travel for a warm weather camp in Turkey before home and away games with Ireland.
If Wales were to win all four warm-up matches, they would equal the world record set by both New Zealand and England which stands at 18 games unbeaten.
“You want to win all your matches, but I don’t think Warren will be thinking too much about the 18-game winning run,” said Williams, one of Welsh rugby’s heroes of the 1970’s.
“Wales are definitely one of the fittest sides in the world, if not the fittest. They undergo some brutal sessions and there is no stone left unturned by modern sides now.
“I saw a video the other day of Fiji doing pre-season training. Even they’re at it!
“Wales base a lot of their selection on what happens in training. In my day that was irrelevant! If our selection was based on training Sir Gareth Edwards would never have had a cap!
“I’d like to see Wales beat England in Cardiff as that is always a huge game for any Welsh rugby fan, but results are not the be all and end all.”
