Web sites for President Bush's campaign and the Republican National Committee (search) suffered outages for several hours on Wednesday.

It was not immediately clear whether a systems failure or a hacking attack was to blame. Campaign and committee officials would only say they were investigating.

The sites began experiencing problems about 11 a.m., according to two companies that monitor Internet performance.

AlertSite.com (search), which had monitors probing the sites every 15 minutes from six U.S. locations, said it took more than three times as long to load the Bush site after 11, and nearly half the attempts were completely unsuccessful. By 1 p.m., the site appeared completely offline.

The site was mostly restored after 5:45 p.m., the company said.

The Republican National Committee site also took longer to load and was sporadically inaccessible, though it didn't appear to go completely offline and was back to normal by 5 p.m., said Ken Godskind, AlertSite's vice president of marketing.

Keynote Systems Inc., which polled the sites from 25 U.S. location every hour, also reported similar trends.

Neither company saw any performance issues with John Kerry's Web site or with the Democratic National Committee's.

Protesters often attempt to bring down sites by overwhelming them with so much bogus traffic that legitimate visitors could not get through. The fact that two sites suffered outages simultaneously suggests such a coordinated attack.

But analysts with AlertSite and Keynote (searchsay other evidence suggests a technical problem.

Roopak Patel, senior Internet analyst for Keynote, said many of the errors related to the Domain Name System, the computers that translate a domain name into a site's actual numeric address. Those errors often occur when incorrect or incomplete information is loaded into the system.