Chairman William Proxmire (D-Wisc.) of the Senate Banking Committee yesterday chided three bank regulatory agencies for "the inordinate length of time" they have taken in preparing a questionaire on banking practices requested by his committee Aug. 31.

The questionaire, which was supposed to be mailed to all commercial banks by Oct. 1, asks the bankers for details about loans made to buy stock, loans to bank insiders and overdrafts.

Proxmire has long been interested in these banking practices, but they have gained immediacy from the revelations of the financial dealings of Bert Lance, the former budget director.

The survey will help the banking committee determine whether legislation should be introduced to prohibit inside dealings by bankers.

Proxmire was replying to an Oct. 17 letter, signed by George LeMaistre, chairman of the Federal Deposit Insurance Corp., John Heimann, Comptroller of the Currency, and J. Charles Partee, a governor of the Federal Reserve Board.

The regulators also sent along a draft of the questionaire for Proxmire to review.

Among the information requested in the survey:

Details of loans of $25,000 or more secured by domestic bank or banking holding company stock.

Loans outstanding to executive officers, major stock holders and directors of other banks, or to their business interests or their families.

The details of overdrafts of $500 or more.

In their letter to Proxmire, the regulators suggested that the bankers be asked to reveal only the amount of overdrafts outstanding on Sept. 30.

But Proxmire countered that each bank should reveal the average amount of overdrafts outstanding daily (or monthly) for the period of Jan. 1, 1977, to Sept. 30, 1977.

A banking committee aide said yesterday that one reason that the single date of Sept. 30 was unacceptable was because by that date many bankers presumably would have covered overdrafts as a result of the furore created by the Bert Lance effort.

By using the nine month period, he said, "we will be able to see what happened both before and after the Lance story broke."