有ed的是被动形式
某人/某物被认为是。。。
sb./ sth. be regarded as sth.=sb./sth. be considered as sth.
this is regarded as a small thing
而原形是表示动作主动发出的
sb. regard sth. as sth. 某人把某物当作。。。
he regards this as a small thing.
根本没后一种搭配
没有be regard as这种搭配,be和regard都是动词,不同时存在