Apparatus, and an associated method, for forming a UDP-Lite, or other, data packet with multiple, dynamically-selected, checksum-protected parts. Digitized data is provided to a formatter, and the formatter forms the data packet to include header fields identifying parts of the payload portion of the data packet that are checksum-protected with different checksums. Additional indicia is contained in the header part of the data packet to identify the checksum-type and the checksum-values associated with the separate parts of the data packet. Multiple, contiguous parts of the data packet are checksum-protected with selectable checksum-types, selected by a selector that operates to control operation of the formatter.