The pair received their first senior call-ups earlier this month for the Prinicipality's training camp in Portugal and have made the cut for the qualifiers.
Also included in Ryan Giggs's squad is Reds keeper Adam Davies - who is understood to be close to finalising a move to Stoke City - and Rotherham United captain Will Vaulks.
But there is no place for Barnsley's out-of-contract winger Ryan Hedges, who was named in the squad for the training camp.
Leeds United's Tyler Roberts also misses out, with the forward having undergone a minor knee operation.
Moore, Williams, Manchester United midfielder Dylan Levitt and Swansea defender Joe Rodon are the only uncapped players selected.
Aaron Ramsey and Ben Davies have been left out of the squad.
Juventus-bound midfielder Ramsey was expected to be absent having not played for Arsenal since damaging a hamstring on April 18, while Tottenham want to assess left-back Davies' recurring groin injury following Saturday's Champions League final.
Star forward Gareth Bale, who has not featured for Real Madrid for the last month amid rumours of a fall-out with club manager Zinedine Zidane, is included in the 28-man selection.
Swansea winger Daniel James, who has been heavily linked with a move to Manchester United, returns after missing the Portugal training camp earlier this month through compassionate leave following the death of his father.
Wales, who sit second in Group E with maximum points following their opening game, face Croatia on June 8 in Osijek, before travelling to Budapest to play Hungary three days later.