Banks, although under heavy pressure from the Carter administration in the final days of the campaign, are finding it harder and harder to hold their prime lending rates to 14 percent as the cost of obtaining funds rises sharply each day.

"Were it not an election year, the prime rate already would be at 15 or 19 percent," according to Lawrence Kudlow, chief economist at the big brokerage firm Bear, Stearns Inc.

Banks have been critized severly by both the president and his top economic advisers for raising their interest charges, and most Wall Street observers agree that banks would like to hold off on a further increase in the highly publicized prime rate until after election day.

"But don't be surprised if the rate goes up before Nov. 4," said one industry insider.

A week ago banks were paying about 12 1/2 percent to borrow money they then lend to their customers. The rate was higher than 14 percent at periods today. Normally there is a spread of between 1 and 1 1/2 percentage points between the cost of obtaining funds and the price of which banks lend them out. b

Already a number of major banks have increased their broker loan rates -- the interest they charge securities firms that borrow overnight to finance stocks and bonds that both the firms and their customers buy on credit. Usually increased in the broker loan rate are a prelude to an increase in the prime rate, the interest banks charge their best corporate customers for a short-term loan.

Most banks borrow their funds by issuing large certificates of deposit that mature in one, two or three months. For several weeks banks had been holding off selling the longer-term certificates, believing that short-term interest rates would come down. But in the last few days, dealers said, banks have been selling the three-month certificates more readily, apparently believing that a tighter monetary policy on the part of the Federal Reserve Board will push rates up during the coming months.

Although Carter and Treasury Secretary G. William Miller have argued that the high bank rates threaten to undermine the fledging economic recovery, a 14 percent prime rate appears to have done little to deter companies from borrowing.

According to the Federal Reserve's own figures, short-term credit demands by companies have been rising sharply in the last six weeks.

"Banks have to depend upon the rate of interest to push borrowers away from the trough," according to Patrick Savin of Drexel Burnham Lambert Inc.

Banks have been less willing than normal -- because of political pressure -- to use interest rates to reduce loan demand, but bankers say privately that part of their reluctance comes about because they are trying to capture some corporate business that in past years had gone to the so-called commercial paper market.

Commercial paper is little more than a corporate IOU, an unsecured promise to pay which one company in need of cash sells to another company or an institution (such as a pension fund or an insurance company). Normally only the biggest and soundest companies can issue commercial paper, and the rates are usually lower than on bank loans.

The surge in interest rates in recent weeks has struck the long-term market as well as the short-term market. Companies and municipalities have cut back or canceled many of the bond issues they had planned because of high rates and the reluctance of investors to put their funds into long-term securities during periods of high inflation.

Analysts are hard-pressured to explain the surge in interest rates during the last week.

"A sweeping inflation fear is begining to build up again," according to Kudlow of Bear, Stearns.

Whatever the explanation, the fact is that bank costs are accelerating, and -- whatever accomodations bankers may want to make to the administration -- economic reality is butting in.

"I'd say they'll be able to resist another four working days," said Kudlow.

That would be until Nov. 4.