From your sample data/output it's not quite clear to me what you mean by "group on A and D"... but here's something that groups by A alone:

#!/usr/bin/perl

my %groups;

while (<DATA>) {
    my ($grp, @other) = split ' ';

    for my $field (@other) {
        my ($name, $val) = split /:/, $field;
        
        if ($name eq "STR") {
            $groups{$grp}{$name} = $val unless defined $groups{$grp}{$
+name};  # first
        } elsif ($name eq "END") {
            $groups{$grp}{$name} = $val;    # last
        } elsif ($name eq "CNT") {
            $groups{$grp}{$name} += $val;   # sum
        } else {
            $groups{$grp}{$name}{$val}++;   # unique values
        }
    }
}

#use Data::Dumper;      # debug
#print Dumper \%groups;

for my $grp (sort keys %groups) {
    my $fields = $groups{$grp};
    
    print $grp;
    for my $name (qw(B C D)) {
        my @elems = keys %{ $fields->{$name} };
        my $val = @elems > 1 ? "MULTIPLE" : $elems[0];
        print "  $name:$val";
    }
    for my $name (qw(CNT STR END)) {
        print " $name:$fields->{$name}";
    }
    print "\n";
    
}

__DATA__
A:1  B:2  C:3 D:4  CNT:1 STR:1 END:2
A:1  B:7  C:3 D:4  CNT:1 STR:2 END:3
A:1  B:2  C:3 D:4  CNT:1 STR:3 END:4
A:2  B:2  C:3 D:5  CNT:1 STR:4 END:5
A:2  B:2  C:3 D:5  CNT:5 STR:5 END:10
A:3  B:2  C:3 D:4  CNT:1 STR:11 END:12
[download]

Output:

A:1  B:MULTIPLE  C:3  D:4 CNT:3 STR:1 END:4
A:2  B:2  C:3  D:5 CNT:6 STR:4 END:10
A:3  B:2  C:3  D:4 CNT:1 STR:11 END:12
[download]

(STR and END are assumed to be sorted on input — in case they aren't, you'd need to compute the minimum and maximum value instead of taking the first and the last...)