With the battle over an initiative to ban gay marriage apparently tightening, $3.6 million in large contributions has poured into the No on Proposition 8 campaign in the past week — narrowing the huge fundraising advantage enjoyed by proponents of the measure.

The developments set up what is likely to be an intense contest in the final weeks of the campaign, with dueling television and radio commercials over whether California should approve a constitutional ban that would eliminate the right of same-sex couples to marry.

After sounding the alarm last week about its $10 million fundraising deficit, Equality California, the lead organization for the No on 8 campaign, has raised more than $3 million within California since Oct. 6, including a $1 million contribution Tuesday from the California Teachers Association, a Mercury News review of Secretary of State’s Office campaign records shows. Meanwhile, out-of-state contributors, including actor T.R. Knight of “Grey’s Anatomy” and financial guru Suze Orman, have made six- and five-figure contributions to Equality California, the umbrella group opposing Proposition 8.

Since Oct. 6, large contributions to ProtectMarriage.com, the lead group supporting Proposition 8, have totaled just $405,969.

The No on 8 campaign has also received commitments for an additional $4 million in donations that have not been received, said Kate Kendell, a member of the campaign’s executive committee. “That has been extraordinary, and has certainly we think helped us close the gap on the $10 million they had out-raised us, but we are not the least bit sanguine about this.”

While the No on 8 side has gotten big donations from Hollywood luminaries like Brad Pitt, Steven Spielberg and Knight, the Yes on 8 side has a media star, too, and not an expected one: San Francisco Mayor Gavin Newsom.

Mining snippets of an enthusiastic Newsom speech where he proclaims, “this door’s wide open now” for gay marriage, “whether you like it or not,” the Yes on 8 campaign has turned him into a figurehead of TV and radio ads that are “picture perfect” for their audience, said David McCuan, a Sonoma State University political science professor who specializes in California ballot initiatives. The Newsom spots have been such a good foil for the Yes on 8 campaign that opponents may be forced to raise even more money to counter them, McCuan said.

Newsom was in the headlines again over the weekend, as conservative groups pointed out that a San Francisco first-grade class went on a field trip from school because their teacher was marrying another woman at City Hall — a ceremony officiated by the mayor. The class didn’t attend the actual ceremony, but waited outside on the steps of City Hall to congratulate their teacher.

Newsom “bought them more free media than the yes side would ever have the money to purchase,” McCuan said. “And conversely, he’s raised the dollars, the cost, for his supporters. He just raised the bar for the amount of money they would have to bring in, and I would argue he’s changed the game.”

The story about a grade-school class being excused from class for a same-sex wedding “proves we’re not lying” in saying that elementary school students will be taught about same-sex marriage in the public schools if voters reject Proposition 8, said Chip White, a spokesman for the Yes on 8 campaign. “This is real; this is happening.”

State school officials say those charges are misleading because local authorities have full control over what is taught about marriage.

In a typical initiative campaign, opponents have the easier case to make, political scientists say, because all they have to do is inject enough doubt into voters’ minds about the proposed change. So, typically, opponents don’t have to match the spending of supporters.

But because same-sex marriage so recently became the status quo in California, the yes side in Proposition 8 can take the traditional opponent position of injecting doubt about change, a strategy supporters of a ban are clearly pursuing.

“That is a fundamental shift,” McCuan said.

When the two key political organizations in the Proposition 8 campaign filed their fundraising reports with the state Oct. 6, ProtectMarriage.com, which wants to ban same-sex marriage, had raised $25.4 million through Sept. 30, compared with $15.8 million for Equality California (noonprop8.com). Data on campaign contributions since then only includes donations of $1,000 or more. But among those big donors, the No on 8 side enjoys a 9-to-1 edge in contributions since Oct. 6.

The national dynamics of the presidential race, with Republican nominee John McCain apparently trailing Democrat Barack Obama, could be providing a fundraising boost for the Yes on 8 side, said Larry Gerston, a political scientist at San Jose State University.

“For those folks on the evangelical side, who have no place to put their money because they have pretty much given up on the McCain campaign, which they didn’t like in the first place, this becomes a great place to put their resources,” Gerston said.

With the campaign now in its final three weeks, donations coming in now are critical for both sides.

“This is the time when the no side needs to be striking back,” McCuan said. “The spots the yes folks have been running have been so picture-perfect for the voters they are talking to that the no campaign needs to not just energize their voters, they need to cut through the clutter on the yes side.”

Contact Mike Swift at (408) 271-3648 or at mswift@mercurynews.com.