The 27 year old will join the Merseyside club in the January transfer window having been granted permission by Los Angeles Galaxy.
"Hopefully he is the first of two or three we want to bring in in January.
"We need to strengthen our squad to make sure we are not in a situation like we have at the moment with so many injuries.
"Landon will certainly add pace, he is a good finisher.
"He was voted best player, yet again, in the American league and is captain of the USA national team.
"I need players who can hit the ground running, who I think can go into the team quite quickly and make an impact.
"With his experience and the goals he has scored, I am hoping he will be able to do that."
Donovan, like Galaxy team-mate David Beckham, has been allowed to join a European club on a short-term deal before the new Major League Soccer season starts in March.
Moyes said: "He is only going to be with us two and a half, maybe three months, so it is a short time to make an impact, but I brought Brian McBride to Preston in a similar situation and he made an impact.
"I then brought him to Everton and he made an impact here.
"We couldn't sign him because we had Kevin Campbell and Duncan Ferguson here at the time but he went on to sign for Fulham and was a really good servant for them."