Republican National Chairman Bill Brock yesterday said recent polling data point to the possibility of a banner GOP year in 1980. But he warned that unauthorized, independent efforts for Ronald Reagan could "fragment the campaign" and cost Republicans their opportunity.

Brock criticized the "independent expenditures" plans of various Reagan supporters, as William J. Casey, director of the official campaign organization for the prospective GOP presidential nominee, announced several aides to former president Gerald R. Ford will take major posts in the Reagan campaign.

In a breakfast meeting with reporters, Brock tipped his hand a new GOP national poll, which he said shows Republicans running almost even with Democrats in voter preference for the 1980 congressional elections.

According to Brock, the survey by Robert Teeter of Market Opinion Research Corp. in Detroit gave the Democrats only a 52-48 percent lead over the GOP, which he said was the best showing for the Republicans since 1966. t

"On every major issue except unemployment, where we broke even, it's an advantage to be a Republican," Brock said.

Others in the GOP hierarchy cautioned that these were partial results and subject to interpretation. But the party chairman coupled them with public polls showing Reagan 10 points ahead of President Carter and said they pointed to the possibility of a great year for the Republicans.

But Brock said he was "extremely concerned" about announced plans by several groups of Republicans, operating independently of Reagan campaign, to raise and spend millions of dollars in behalf of the former California governor's candidacy. Such expenditures have been allowed by law as long as they are not done in cooperation with the official campaign, but Common Cause, a public advocacy lobby, is expected to announce a legal challenge to them today.

Brock said he opposed the half dozen separate pro-Reagan committees on political grounds, asserting they could lead to a "fragmented, confused, disorganized" campaign.

"If they emphasize different issues than Reagan wants to emphasize, if they run ads that are factually inaccurate, they force us to disavow them -- and that's divisive," Brock said.

The chairman said he doubted the independent committees, some headed by well-known Republican officeholders and veterans of the Nixon and Ford administrations, could raise the millions of dollars they have talked about.

But he said that if they succeeded, there would be "a draining of funds for the grass-roots party building" and the support of GOP candidates for offices lower on the ballot.

He accused the promoters of these groups of acting as if "we're going to elect one person and change the whole goldarn world."

In urging Republicans interested in Reagan to contribute to the GOP's official campaign committees, Brock said he thought Reagan's high-command had the same view of the independent efforts he expressed.

But Casey, Reagan's campaign director, took a noncommittal stand at his press conference later in the day.

"I won't discourage anyone from exercising their constitutional rights," Casey said. "How helpful it is remains to be seen."

Casey did condemn efforts by some conservative groups to kill Sen. Howard H. Baker Jr.'s (Tenn.) vice presidential prospects, calling such activity damaging to Republican unity and the Reagan campaign.

Casey formally announced that two former officials of the Nixon and Ford administrations, Washington lobbyist William Timmons and lawyer James T. Lynn, would join the Reagan campaign. Timmons will be deputy director for campaign operations and Lynn the general counsel.