The San Diego Convention and Visitors Bureau, supported by hotel taxes, will spend nearly $300,000 to buy TV time for the Republican National Committee. The RNC will air the party's own version of the Republican National Convention on three cable networks the week of Aug. 12. The surprise announcement was made today by Republican National Chairman Haley Barbour, who said that the GOP TV coverage would include information about the city. Republicans will produce two hours a day of coverage Monday through Wednesday that will air on the Family Channel and NewsTalk Television, three hours on Thursday and a one-hour wrap up on Friday. In addition, a half-hour show will air mornings on the USA Network. Mr. Barbour said the RNC decided to act because it was uncertain whether CSPAN or broadcast networks would air both live activities at the convention and the extensive taped issue-oriented programming that would be shown to delegates. He said GOP TV's "Unconventional Convention" would air both.