With an ease that seems to border on abandon, major banks are putting together record-sized lines of credit for big companies that are stalking takeover targets and for slightly smaller concerns who might wield the credits to defend their independence.

Mobil Corp., which said it may be interested in buying beleaguered Conoco Inc., is arranging a $5 billion credit line through a syndicate of banks headed by Citibank.

E. I. du Pont de Nemours, which had made an offer for Conoco (and which is Conoco's preferred suitor), arranged $3 billion in loan commitments last week and another $1 billion this week. Texaco reportedly has a line of credit of $5.5 billion it was putting together last week, while Pennzoil can draw up $2.5 billion from its bankers. And Marathon Oil Co., said to be a takeover target, revealed today it is lining up a new credit line through a Chase Manhattan syndicate.

Conoco is taking no chances that White Knight Du Pont will give in to the Canadian distiller Seagram (which has made an "unfriendly" bid for Conoco) or Mobil, should it make an offer. The Stamford, Conn.-based Conoco has arranged a $3 billion credit line of its own that could be used to buy its own stock in an attempt to thwart a takeover. Merely the threat that a company might turn a $3 billion line of credit into a $3 billion liability is enough to turn some potential buyers off (although apparently not Seagram, which is in the middle of a hot bidding war with Du Pont).

For the most part, the companies, whether pursuer or pursued, are all knocking on the same doors. "The faces in each of the syndicates are the same. We're involved in every one of the big deals you've read about in the newspapers," said the chief lending officer at one of the nation's biggest banks.

So far, nearly all the lines of credit have not been drawn on.The takeovers have not reached the stage where the pursuing company has had to buy stock from the shareholders in the target corporation. In the meantime, the companies pay the banks a commitment fee, usually between one-quarter percent and one-half percent a year, until they turn the loan commitment into a loan.

But the huge loan commitments already made have some analysts worried that when the commitment becomes a loan, strong upward pressures will be exerted on interest rates both in the United States and abroad as banks raise money in the so-called open market that they then lend to the companies.

Seven companies alone have loan commitments totalling $24.9 billion.

In Washington today, House Banking Committee Chairman Fernand St Germain (D-R.I.) asked the Federal Reserve Board to take steps to curb what he called "excessive use" of the nation's credit to fuel takeovers of energy concerns. In a letter to Fed Chairman Paul Volcker, St Germain said many segments of the economy are near collapse in a period of "highly restrictive money policy."

But severe credit limitations imposed on housing and small business are "not shared by the huge oil companies who desire funds for an international game of monopoly," St Germain complained.

However, Richard Peterson, chief economist for Continental Illinois National Bank, cautioned that the real pressure that these lines of credit would create, if exercised, is exaggerated.

Because many of the lines of credit were taken out by companies gunning for the same target, Conoco, there is "no way that all of the lines are going to be used," Peterson said.

Furthermore, at the same time that banks are in the market borrowing money to loan to the companies that eventually draw on their lines of credit, many of the shareholders who sell their stocks will be looking for somewhere in which to invest their new-found cash for the short term, according to Bank of America economist Frank McCormick. A sizable portion of the cash will find its way into the certificate of deposit and commercial paper markets, precisely the arenas where the banks will be raising funds. That should temper upward pressure on rates, McCormick added.

If all else remains equal, even the drawdown of one of the biggest lines should add no more than 10 or 20 basis points to short-term interest rates, he said. A basis point is one-100th of a percentage point.

Nevertheless, Peterson conceded that what is reality in the long run and what is reality in the short run often is different. All markets -- stock, bond or money -- operate on perceptions.

Bankers themselves say privately that they wish the companies weren't knocking at their doors. The business isn't all that profitable and, because of the sums involved, putting the lines of credit together takes up a lot of time of senior lending officials, they point out.

Banks officials say they are participating in the commitments in order to maintain customer relationships for the future.

Curiously, although most of the banking syndicates are led by U.S. banks, most of the money will come from foreign banks.

Because U.S. laws sharply restrict the amount of money any individual bank can loan one company, the less-tightly-related European and Canadian banks are promising to ante up most of the cash should the credit lines be drawn down.