WASHINGTON — The national Republican Party sued the Federal Election Commission yesterday, seeking to overturn prohibitions on unregulated corporate and labor contributions and to make it easier to coordinate spending with federal candidates.

In two lawsuits, the Republican National Committee directly challenged post-Watergate restrictions on the ability of parties and candidates to work hand-in-hand on political campaigns and the law Congress passed in 2002 banning unlimited contributions know as “soft money.” The lawsuits were filed in Louisiana and Washington, respectively.

RNC Chairman Robert M. “Mike” Duncan said in an interview that the suits were designed to “strengthen the Republican Party and bring a more level playing field to campaign finance.”

At issue are two distinct laws — one passed in the aftermath of the Watergate abuses of the early 1970s and the other a six-year-old ban on soft money. Both laws have been upheld by the Supreme Court, but since then the Court has a new chief justice in John G. Roberts and a new justice in Samuel Alito.

The lawsuits come after the defeat of Republican presidential candidate John McCain, one of the authors of the 2002 Bipartisan Campaign Reform Act and a fierce opponent of soft money — that is, unlimited money from corporations, unions and wealthy individuals.

The RNC lawsuit filed in Washington said the total ban on soft money amounts to a violation of the First Amendment’s guarantees of free speech and association.

Critics say the suit is merely an attempt by the RNC to test the law against a reconstituted Supreme Court.

“This effort to go to the Supreme Court appears to be based on the idea that we have different justices so the prior decisions should just be thrown out, and that is just dead wrong,” said Fred Wertheimer, president of Democracy 21, a campaign-finance watchdog group.

Through its other lawsuit, the RNC seeks to be able to raise unlimited contributions for “non-federal” activities — that is, for expenditures unrelated to presidential, U.S. Senate or House of Representative elections. The money, the complaint says, would be used to help elect Republicans to state offices, to finance congressional redistricting efforts by state Republican parties following the 2010 census, and to finance lobbying efforts on federal legislative issues.

The RNC’s effort to permit fundraising for state parties and state candidates would reverse a key component of the 2002 law that McCain helped write with Democratic Sen. Russell Feingold of Wisconsin and House members Christopher Shays, R-Conn., and Martin Meehan, D-Mass.

Under that law, the national parties can raise money only under federal fundraising restrictions. If the national parties can raise money for state parties or for state candidates, they would adjust that fundraising to state limits, some of which are far more lenient than federal law.

Since the 1970s, parties also have been limited in the amount of money they can spend in coordination with a House, Senate or presidential candidate. For instance, this year, the RNC and its counterpart, the Democratic National Committee, could spend $19 million each in consultation with the McCain or the Barack Obama campaigns.

For the past decade, national party committees have set up independent expenditure units that can spend money on behalf of candidates as long as they have no contact with each other. The RNC spent more than $50 million against Obama through its independent operation.

“That results in these expenditure units being given money without direction, without coordination,” Duncan said in the interview. “You get results where candidates are often upset with the message that is going out.”