ISBA's latest position has the backing of the UK's biggest advertiser Procter & Gamble.
At its conference last week, ISBA said maintaining the status quo - where a licence-fee-funded BBC is free to compete with commercial rivals for audiences - was not an option. But it is now backing less radical alternatives that will enable its members to continue to take part in the debate in the run-up to the BBC's charter renewal.
Speaking on behalf of ISBA's TV action group, P&G director of external relations Gary Cunningham told delegates he did not want the BBC to be the same as ITV or Sky, but that change was needed to ensure fairer competition.
One option is for the BBC to lose its stranglehold on the licence fee, freeing it to take some advertising to make up for the funding loss.
Under the second option, ISBA is calling for a more clearly defined public service remit for the BBC to stop advertisers losing commercial audiences to it. ISBA is believed to favour requiring the BBC to refocus on public service broadcasting as the more realistic option.
ISBA will submit its finalised proposals to the charter renewal process on March 31.