WASHINGTON — The Republican Party’s strategy since early last year of lock-step opposition to the Obama administration’s major legislative initiatives has proved to be less bankable than some party leaders may have anticipated.

With eight months to go before congressional elections, House and Senate Democratic candidates exceed in virtually every important campaign fundraising category. Democratic House lawmakers appear likely to reverse their seven-cycle record of being outspent by House Republicans, according to recent finance reports.

Democrats in both chambers are enjoying the traditional advantages of majority-party status — and then some. They lead in donations by political action committees, by committees affiliated with the national political parties or with House and Senate leaders, and in individual contributions to incumbent lawmakers. In some instances, their lead exceeds what the Republicans had when that party controlled both chambers in the 2005-06 midterm election cycle.

To no surprise, analysts differ by party on the causes and significance of the disparity. Some Republicans say a donations surge may still come in the campaign’s final months, particularly as their party courts new, small donors outside Washington. They also complain that donations to party stalwarts have been affected by internal squabbles with rebellious tea partiers, which they hope will end soon.

Republicans also say the party must remain unified in opposition to President Obama if it wants to energize the most reliable donors, volunteers and voters. “If we look like winners, money will follow,” said Steven Gordon, an adviser to Senate Republican leaders who in the past has raised $70 million for GOP congressional candidates.

But recent controversy over lavish and questionable expenditures by the Republican National Committee — including chartered airplanes and a young Republicans’ night out at a bondage-themed nightclub in Hollywood — appears likely to complicate efforts by the Republicans to overcome their deficit. Some traditional party supporters, such as Family Council President Tony Perkins, have recently urged followers to respond by withholding donations from the national party.

Democrats say their higher tallies so far are just the beginning, because campaign cash usually follows political momentum and Obama’s health care triumph may have ended a political slide.

“There’s been a real kick-up of wind in Democratic party sails,” said Jonathan Mantz, a former finance director for Hillary Rodham Clinton’s presidential campaign. “Success will breed success.”.

The Republicans’ unified opposition to Obama’s agenda kicked off with a failed attempt early last year to defeat his economic stimulus legislation, and re-emerged during a failed effort last June to block a House Democratic climate change bill. It played out again during the failed attempt to stop Obama’s health care legislation.

But the party’s defiance shows no sign yet of enabling its lawmakers to overcome the traditional financial disadvantage of a minority party, a status that routinely leads to smaller campaign contributions.

For example, the 165 incumbent House Republicans seeking re-election last year on average raised $587,570 over 12 months, while the 245 incumbent Democrats seeking re-election raised an average of $662,793, according to data from the nonprofit Campaign Finance Institute.

At the end of 2005, when Republicans controlled the House, the tallies were almost precisely opposite. Of course, the Democrats went on to gain 31 seats in the 2006 election and regain control of the chamber, so tallies midway through a cycle do not necessarily predict outcomes.

But much of the time, they do.