Presidential candidate Barack Obama has bought advertising in gay newspapers in four cities in the two key primary states of Texas and Ohio.

The Advocate reports that full page adverts will appear in titles in Dallas, Houston, Cleveland and Columbus.

Democratic primary and caucus participants in the two states vote next Tuesday, along with Rhode Island and Vermont.

The delegate-rich Ohio and Texas contests are must-wins for Hillary Clinton, who is trailing Senator Obama in pledged delegates to the nominating convention in August.

“I think if we lose in Texas and Ohio, Mrs. Clinton will have to make her decision as to whether she moves forward or not,” senior Clinton aide Harold Ickes told the Wall Street Journal on Tuesday.

Obama LGBT Steering Committee member Eric Stern told The Advocate:

“It’s a direct appeal to LGBT voters asking for their support.”

In Texas Senator Clinton is polling 47% to Senator Obama’s 44%, with 9% not sure.

In a poll released on Monday, the former First Lady has seen her lead in Ohio collapse over the space of a fortnight from 51% to 37% to 48% to 43%.

In a debate between the candidates on Tuesday Senator Clinton, 60, openly attacked her opponent’s tactics and positions on trade and health care coverage.

She also made reference to the perception that Senator Obama is receiving favourable press coverage.

“I will have a much better case to make on a range of the issues that, really, America must confront going forward, and will be able to hold my own and make the case for a change in policy that will be better for our country,” she told an audience at Cleveland State University and millions watching on TV network MSNBC.

Senator Obama, 46, accused her campaign of constant “negative attacks” and smiled at her criticisms of his lack of foreign affairs experience.

He responded that she had voted with President Bush on the Iraq war.

“So the same person that she criticises for having terrible judgment, and we can’t afford to have another one of those, in fact she facilitated and enabled this individual to make a decision that has been strategically damaging to the United States of America.”