Ponting is due to lead Australia in the Ashes Test series in the second half of the English summer and 35-year-old former Sri Lanka skipper Jayasuriya, an aggressive left-handed batsman, is set to be available for five County Championship matches as well as several One-day fixtures.
Somerset chief executive Peter Anderson said: "This is a very exciting short-term signing. His (Jayasuriya's) availability has to be ratified by the Sri Lanka Cricket, but we are not anticipating any problems."
Jayasuriya's contract is set to last until the end of May when South African captain Graeme Smith is due to take over.
In 94 Tests Jayasuriya has scored 6,388 runs with 14 hundreds at an average of 43.45 while in a mammoth 334 One-day Internationals he has 9,924 runs at 31.190 with 18 centuries.
His blazing hitting was a key component of Sri Lanka's 1996 World Cup-winning team and his left-arm spin bowling has often proved effective in both Test and One-day cricket.
Somerset's other overseas registration this year is set to be taken up by West Indies fast bowler Nixon McLean.
The west country side finished fourth in the second division of last season's Championship, missing out on the third and final promotion place claimed by Glamorgan.