Intermittent loss of connection with Internet

Our church's office has a Linksys WRT54G wireless router. However,
the principal use of the router is in the wired mode, i.e., the
desktop PC in the office is connected by LAN cable. The wireless
signal is being broadcast, though, but it is encrypted.

Infrequently, every one to two weeks, there is a dropping of Internet
access. The problem can always be resolved by disconnecting the
computer from the router and connecting it directly to the ISP's
modem. (ISP in this case is Clearwire.) Or, in another case just
yesterday, we experienced a "loss" of Internet service, one of office-
staff members simply disconnected the PC from the router and then
reconnecting it (pull out LAN cable then re-connect). Problem was
solved immediately.

Is this indicative of a problem with the router or a problem with the
ISP?

I am a little mystified by all of this because my service at home, via
cable modem, utilizes a wireless router (though of mfgr Airlink) and I
almost NEVER have a problem like this. So, I know that this is not
something that has to be just necessarily accepted.

Dave4681