I find the verb красть - украсть and looking its conjugation according with my rules of changes in verbs, I find normal that being its root крад- крад-у, -ёшь, ... the final д is suppressed before л in preterite, (and also like with т): вёд-л -> вёл вела, ... OK.
But as for Infinitive I find no rule permitting the change of "д" for "c", however for euphonic reasons some change seems rather necessary. I see the same change in вед-у, -ёшь, ... when it becomes вести.
I ask: can be taken as a rule that д of root (and perhaps even т) should be changed in Infinitive before т into c ? I have no enough vocabulary to consider more verbs that could make clear my doubt. Thanks.