Assuming that the representatives are members of parties, for some reason, and that the proportionality of the committees should reflect the relative sizes of the parties, then the obvious way of assigning representatives is:
Start with the party with the most representatives. Pull out a representative and put it into a committee. Then pull out the next representative and put it into the next committee. Repeat until you run out of representatives.
Repeat with the next most populous party. Continue until all representatives are assigned.
That might not be clear, so an example:
20 Representatives: A B C D E F G H I J K L M N O P Q R S T
Five Committees of four members: () [] {} <> «»
Parties:
Party $ has 10 members: A B C D E F G H I J
Party & has 5 members: K L M N O
Party * has 3 members: P Q R
Party ~ has 2 members: S T
Round 1 of assignment -- starting with Party $:
Round 2 of assignment -- continuing with Party $:
(A F)
[B G]
{C H}
< D I >
«E J»
Round 3 of assignment -- finished with Party $; starting with Party &:
(A F K)
[B G L]
{C H M}
< D I N >
«E J O»
Round 4 of assignment -- finished with Party; starting with Party *:
(A F K P)
[B G L Q]
{C H M R}
< D I N >
«E J O»
Round 5 of assignment -- finished with Party *; starting with Party ~:
(A F K P)
[B G L Q]
{C H M R}
< D I N S >
«E J O T»
And then we're done.