Robert H. McKinney, the jack-of-most-trades from Indianapolis who has become President Carter's controversial nominee to head the Federal Home Loan Bank Board, withstood pointed questioning in the Senate yesterday over alleged conflicts of interest and loan discrimination in the operation of the savings and loan association he chairs.

Sen. William Proxmire (D-Wis.), chairman of the Senate Banking Committee, called McKinney's thrift institution - First Federal Savings and Loan of Indianapolis - "a textbook example" of interlockings between banking and other professions. The senator expressed "great doubts" about whether McKinney "can be a regulator in the public interest."

McKinney's resume reads like a one man Who's Who of Indianapolis. In addition to being chairman of the second largest S&L in Indiana (asserts: $335 million), he is a senior partner in a law firm that represents First Federal, among other clients, and he is chairman of Jefferson Corporation, which sells primarily insurance and building supplies through 10 subsidiaries.

McKinney also was a classmate of President Carter's at the Naval Academy and headed Carter's campaign in Indiana.

Proxmire claimed McKinney's nomination violated the spirit of a campaign pledge Carter made to do something about what Carter called "the sweetheart relationship" between federal commissions and the industry they regulate. "This is a tough nomination for us," Proxmire said.

Public opposition to McKinney's confirmation has been strong, coming mainly from consumer organizations, urban leagues and labor groups. Several of McKinney's critics are scheduled to testify Monday.

The nomination, too, seems to have strained relations among some committee members, a couple of whom voiced concern that McKinney was being overly examined and perhaps abused.

Sen. Jake Garn (R-Utah) praised McKinney's talents and termed him a "superb nominee." He said that if members of Congress had to make as many disclosures as McKinney has, "a lot would decide not to carry on."

"The only thing that's wrong with your nomination," Garn added, "is that you're successful, you've accomplished something, you're brilliant."

Last Monday, 17 federal auditors appeared unexpectedly at First Federal to begin a four-day exhaustive audit. The auditors, McKinney said, told him they were there in conjunction with a national investigation of S&L's. The examination, they reportedly told him, had notheing to do with his nomination.

Sen. Richard Lugar (R-Ind.), a former mayor of Indianapolis and McKinney supporter, termed the investigation "almost harrasment." Suggesting the investigators may have been sent by Rep. Benjamin Rosenthal (D.-N.Y.), who has staunchly opposed the nomination, Lugar insisted the committee at least learn the results of the probe.

"An attempt was being made once again to discourage this nominee from proceeding," Lugar charged. "Once again, he has withstood another assault.

Throughout the long day of testimony, McKinney repeatedly denied the two major allegations against him - that his thrift institution has been guilty of refusing loans to low-income neighborhoods, and that he is, in Proxmire's words, "an industry man."

Speaking to his own career, McKinney said he has been careful to avoid any conflict of interest. "There is no connection whatsoever between the S&L and Jefferson Corp," he said, "other than the fact I head both. No referrals are made by the S&L to Jefferson or the law firm. That's not the way we do business."

The senators quoted back to McKinney two letters he had written to the Federal Home Loan Bank Board, containing objections to proposed regulations to prohibit realtors, property lawyers and theirs with possible conflicts of interest from serving on S&L boards, and to another set of proposed rules that would have required full disclosure by S&L board members.

McKinney said he does favor a disclosure rule for S&L's, but opposed one several years ago because he thought it would be used as a substitute for vigorous regulation by the Board.

Pressed for his views about conflict of interest situations, McKinney said he still opposed a blanket rule banning the hardship such a rule would impose on small towns with limited financial talent.

As to the loaning practices of First Federal, McKinney disputed charges that the S&L has loaned a smaller percentage of its total mortgage money for shorter terms in the innercity that other major financial institutions in Indianapolis. In fact, he insisted, First Federal has turned down fewer loan requests and lent more money to ghetto areas for longer terms with smaller down payments than other banks and S&L's.

If confirmed, McKinney said he would resign from First Federal and the law firm, and would place hisbusiness in a blind trust.