Major dissident shareholders in McGraw-Hill, Inc. apparently will try to feel out all stockholders in the giant publishing company to see if they are receptive to a $40 a share offer from American Express Co.

Informed sources said the shareholders, reported to include Maxwell Geffen (who owns 100,000 shares) and family member Donald C. McGraw Jr., met most of today to try to decide what action to take, but did not have time to complete the required filings with the Securities and Exchange Commission.

These sources said that unless the dissident shareholders suddenly change their minds, they can be expected to file a notice of their intentions with the SEC early next week.

American Express first offered $34 a share for McGraw-Hill, but withdrew that offer after encountering bitter resistance from the company, led by chairman Harold W. McGraw Jr. American Express told the company's directors it would offer $40 a share, but only on the condition that the company agreed to stand by and not actively try to fight the merger bid.

McGraw-Hill stock closed at $26 a share on Jan. 8, the day before the American Express bid was made public.

McGraw-Hill has been sued several times by angry stockholders who want to consider the American Express offer. McGraw-Hill closed at 28 5/8 today.

Earlier this week it appeared that McGraw-Hill had fended off the American Express bid when Allen & Co., the invesment banking firm approached by Geffen to manage a proxy fight, said it was not interested in organizing a campaign to take control of the publisher away from the current board.

And, although angry that the board had rejected the American Express offer without giving shareholders a chance to decide, neither Geffen nor Donald McGraw appeared to have the heart for what could be a difficult, risky and expensive proxy battle.

The shareholders group is expected to poll McGraw-Hill shareholders first to see if they are interested in American Express' offer. If the results of the canvass are positive, they will try to force the courts to make McGraw-Hill put the offer to shareholders.

American Express has said it will hold the offer open until March 1 and sources close to the company said the offer could be kept open longer than that if it appears shareholders will be able to consider it.