The battle over the nomination of Theodore C. Sorensen to head the Central Intelligence Agency intensified yesterday.

President-elect Jimmy Carter defended the nomination, but Republican National Chairman Bill Brock called it "a major Carter blunder . . . just incredible," and said Sorensen had demonstrated a "total lack of fitness for the job."

Senate Republican Leader Howard Baker (Tenn.) said, "the odds are Sorensen is not going to be reported out (by the Senate Intelligence Committee) and I don't think he should be . . . the CIA director should be above reproach and beyond controversy, and Sorensen is definitely not that person."

Sorensen's confirmation hearing before the Intelligence Committee begins today.

Critics cite-allegations that he leaked and mishandled secret classified materials as a White House official in the 1960s, avoided the military draft by classification as a conscientious objector and then as a father, and may have been involved in assassination plots against foreign officials during the Kennedy administration. Yesterday an aide denied all these charges.

Carter, in a statement from Plains, Ga., called "attacks on Mr. Sorensen's judgement and loyalty groundless and unfair." He defended Sorensen's handling of confidential materials for President Kennedy in the early 1960s as "consistent with what I understand to have been common practice in administrations of both parties."

Sorensen aides said the President-elect assured him in a phone conversation yesterday morning that he has no intention of asking him to withdraw.

They also said Sorensen received a strong endorsement from former CIA Director John A. McCone (1961-65) in a telegram to Sen. Daniel K. Inouye (D-Hawaii), chairman of the Senate Intelligence Committee.

But Brook, asserting that former California Gov. Ronald Reagan (R) shares his opposition to Sorensen, predicted that "Carter will be forced to withdraw the nomination and if he doesn't, the Senate, I am confident, will repudiate it. I wouldn't be surprised to see the committee refuse to report it out."

Brock said GOP opposition to Sorensen is "not a matter of partisan-ship," but added, "If the committee rejects him, it would be a striking repudiation of Carter at this stage - inauguration week."

In his testimony today, aides said Sorensen will say that he "leaked" only with permission of the President, that he had General Services Administration permission to take various documents with him after he left the White House, that he was willing to serve under fire in the military but in a non-combatant role, and that he "knew nothing" of alleged CIA assassination plots.

Opposition to Sorensen from members of the 15-man Intelligence Committee has been emerging over the past two weeks.

Sens. Jake Garn (R-Utah), Barry Goldwater (R-Ariz.) and Strom Thurmond (R-S.C.) apparently are already prepared to oppose him, Sen. Robert C. Morgan (D-N.C.) is highly dubious, Baker is opposed, several other members privately are dubious, and Chairman Inouye also is reported to have advised the President-elect it might be wise to withdraw Sorensen's name.

Yesterday Sen. Spark Matsunaga [WORD ILLEGIBLE] not a committee member but Inouye's Hawaii colleague, was quoted by United Press International as saying "I hope he would withdraw and not embarrass the President."

Carter, it was learned, has personally called several members of the committee in an effort to obtain support for Sorensen.

Meanwhile, Richard Neustadt, Carter transition aide who is helping Sorensen prepare for the Senate Intelligence Committee hearings, outlined the rebuttal Sorensen will offer today.

He said Sorensen will tell the committee that when he was a Kennedy top aide "he knews nothing about any of the alleged assassination plots" by the CIA against foreign government officials.

As for charges that Sorensen was a conscientious objector, Neustadt said Sorensen was classified 1-AO in 1948. "The classification indicates willingness to serve under fire but not to bear arms. It is not a reluctance to be in danger. Combat medics are classifed this way. He received this classification because he personally does not believe in shooting at people. It's not a belief he wants to impose on the rest of society. He just personally didn't want to shoot people at the time." He came from a Unitarian family.

News records indicate that Sorensen was later classified as married, temporarily as 4-F because of a tumor, and then 3-A as a father.

In September, 1961, a critical article on Sorensen's draft classifications was placed in the Congressional Record by Goldwater, who asserted, "It often requires more courage to seek this classification (1-AO) than to serve in the armed forces However, I can't help but wonder at the thought of the fathers and mothers of American boys who right now are being called up for active military service when they learn that one of the President's closest advisors is an objector because of his conscience."

Possibly the greatest threat to Sorensen results from committee reaction to two affidavits filed by Sorensen on behalf of the defense when the government tried to stop newspapers from publishing the secret government Pentagon papers, and the 1972 trial of Daniel Ellsberg, former Rand Corp. associate accused of leaking the papers to the press.

In those affidavits, Sorensen revealed that he took 67 boxes of materials from the White House when he left, including seven boxes of classified materials, used some to write his 1965 book, "Kennedy," received a tax break for donating some of the papers to the government, and while in the White House leaked classified materials to the press.