WASHINGTON - Barack Oba-ma is going for the gold. The Democratic presidential contender has decided to buy $5 million in national advertising on NBC during the broadcast of the Olympic games. The ads will appear on network and cable channels.

The Olympics, to be held in Beijing, China, will open Aug. 8. Such an extensive purchase of ad time would give Obama wide exposure before the Democratic National Convention, to be held the last week in August.

Obama has the resources: He has set fundraising records and reported raising $52 million in June, more than twice the $21.5 million raised by his Republican rival, Sen. John McCain.

At the same time, the expenditure is as significant for its reach as for its bold statement.

Obama has aired ads in 18 states, including states that have traditionally voted Republican in presidential elections, including Alaska and Virginia.

A national network ad is unusual in politics, because of its expense and because it reaches audiences not necessarily targeted by a campaign. *