Saying it wants to avert Water-gate-style campaign finance abuses, Common Cause went to court yesterday to stop a committee from raising and spending up to $30 million to promote Ronald Reagan's presidential candidacy.

Common Cause, a public advocacy lobby, said the recently announced effort by Americans for a Change was designed to get around Congress' intent to finance presidential campaigns mostly with federal funds. The nominees of the two major parties will receive $29.4 million each this year.

"Congress sought to put behind us forever the old pre-Watergate abuses of the power of money in elections," said Archibald Cox, the original special Watergate prosecutor, now chairman of Common Cause.

"The so-called independent expenditures challenged by this suit threaten to unravel that whole system of laws to eliminate the influence of money in political campaign and returns us to the day characterized by the old Watergate abuses," he said.

Sen. Harrison Schmitt (R-N.M.), chairman of Americans for a Change, said his committee has acted in accordance with the law and will continue to do so.

"It is clearly a First Amendment right to advocate one candidacy over another," he said. "It is one way in which a challenger can balance the power of the incumbency."

Schmitt announced the committee plans to raise and spend between $20 million and $30 million independently of the Reagan campaign. But Common Cause charged in the suit that the fund-raising group "is closely linked . . . to the Republican Party, the Republican National Committee and the Reagan campaign organization."

Monday, Republican National Chairman Bill Brock said that unauthorized, independent efforts for Reagan could lead to "fragmented, confused, disorganized" campaign.

To the eligible for federal funding, a candidate must certify he will not accept private contributions for his campaign and will spend no more than the government allow. But federal election laws permit the raising of funds on a candidate's behalf by an independent organization, as long as it has no ties to the candidate's campaign organization.