By Ross Kerber

BOSTON, Sept 24 (Reuters) - Top U.S. companies are reporting more detail about their political contributions, according to a survey by the Center for Political Accountability, a trend that won praise from the group, which pushes for greater transparency.

In a survey provided to Reuters ahead of its scheduled release on Wednesday, the Washington-based organization scored 191 companies on a complex scale that tracked actions such as whether they disclose corporate contributions to political candidates, parties or trade associations. Such spending can be controversial amid the broader debate over campaign-finance rules.

Researchers found the average score rose to 56.4 from 51.0 in 2013 among the companies, all in the top 200 of the S&P 500 index.

"Companies are recognizing disclosure as good governance," said CPA President Bruce Freed. "Disclosure means that companies and shareholders know how their money is being used" to influence policy debates.

The companies that improved their scores include railroad operator CSX Corp and semiconductor equipment maker Applied Materials Inc. Both provide lists of recent contributions to political candidates and to trade groups, including the U.S. Chamber of Commerce.

Another company with a higher score was asset manager BlackRock Inc, which recently said it restricts contributions - such as not spending money on certain advertisements that back a particular candidate just before an election.

Freed and his organization have been at the center of efforts to require companies to disclose more about their spending. But the push has drawn criticism from business groups, who say more disclosures offer little of value to shareholders.

James Copland, senior fellow at the Manhattan Institute, a free-market think tank, said requiring more disclosure will effectively give companies less influence on public policy.

"Whether that is good or bad in the aggregate is debatable, but from a shareholder perspective, it's against your interest," Copland said.

Restrictions on political spending are in decline after the U.S. Supreme Court's 2010 Citizens United decision, which allowed unlimited spending by independent groups in federal elections as a form of free speech.

The U.S. Securities and Exchange Commission has not acted on calls by Freed's group and others to require more corporate disclosure.

Without SEC action, debate has shifted to shareholder resolutions calling for such changes. In 2014, 86 of these resolutions on average drew 24.5 percent support, according to proxy adviser Institutional Shareholder Services.