Senate Majority Leader Robert C. Byrd (D-W. Va.) said yesterday that the special counsel investigating President Carter's family warehouse business must be given a stronger, written guarantee of his independence.

In a Senate floor speech Byrd called for a charter providing "explicit protection against removal except for extraordinary improprieties."

Paul J. Curran, who Tuesday was appointed special counsel by Attorney General Griffin B. Bell, said yesterday he was confident that he could conduct an independent investigation.

"I have assurance of total independence in the investigation -- my own staff -- and I'm going to call the shots as I see them," Curran said at a news conference held in his Park Avenue law offices in New York.

Immediately after Currant's appointment as special counsel, key Republicans criticized the Justice Department for not granting Curran full special prosecutor powers. Unlike a special prosecutor, Curran does not have the authority to seek indictments of suspects or immunity for witnesses without Justice Department approval.

Byrd, in his speech, said he was "disappointed that the Justice Department concluded that the special posecutor legislation did not apply in this situation."

Justice Department officials said that legislation passed by Congress last October providing for appointment of a special prosecutor does not apply in this case because the investigation was started before the law was enacted.

Bell, however, appointed Curran under the same law that was used to name Watergate Special Prosecutor Archibald Cox in 1973, and Bell has the power to grant Curran as much independence as Cox had.

The Carter warehouse investigation grew out of a grand jury probe of the banking affairs of former Office of Management and Budget director Bert Lance. A grand jury has been hearing testimony for more than a year.

Curran, at his news conference, admitted that some important details of his investigation remain undefined. But he said he expected to get a "written mandate" from Justice.

Asked whether the full results of the investigation would be made public, Curran said he was uncertain that they would be.

The FBI recently conducted an intensive three-week investigation of the loans from National Bank of Georgia in Atlanta to the Carter warehouse in Plains, Ga.

The $6.5 million in loans were arranged by Bert Lance in 1975, shortly after he became president of NBG.

The FBI reportedly found possible violations of banking laws because repayments of the NBG loans were late.

Among the questions facing Curran and his team is what happened to the money in warehouse accounts that wasn't being used to repay NBG.

Questions were raised as to whether any of the money found its way into the 1976 Carter presidential campaign. However, there's been no indication that any such diversion occurred, and the White House has repeatedly denied that this nappened.

Curran made it clear, however, that his investigation would go beyond the question of whether warehouse money was diverted to the campaign.

He said that even if he found no wrongdoing involving the 1976 campaign, hr would still pursue the investigation to its conclusion. This means the investigation will probe the financial dealings of the president's brother, Billy Carter, who managed the warehouse operation through the summer of 1977.

The warehouse is currently being run by a management company, and the president's 62 percent interest is in a blind trust under Atlanta attorney Charles Kirbo.

Asked if he would question President Carter or the president's mother or brother if it became necessary, Curran said repeatedly that he would question anyone who could shed light on the warehouse finances.