Uncle Sam, sorely strapped for money in the face of mounting inflation, is doing just what any private citizen would do in a pinch -- he's looking at his account books to see who owes him money.

For the first time in memory, the Office of Management and Budget is preparing a major review of federal debt collection practices in hopes of cracking down on defaults and speeding up some payments.

OMB director James T. McIntyre said yesterday the agency was acting out of concern over the rapid growth of government lending in recent years and indications that defaults in some areas may be getting out of hand.

Although the figures still are sketchy, OMB estimates that debt owed to the federal government has almost doubled over the past five years, rising from $77.6 billion in fiscal 1974 to $140.6 billion in fiscal 1978.

One recent example has been the scandal involving defaults on student loans. Of some $4.4 billion in loans the government has guaranteed since 1965, the U.S. has paid some $658 million in defaults.

Under current procedures, the government has no system for fullfledged management of such debts. Officials don't know how many borrowers there are in total, how many defaults there have been or how long the loans have been out.

The review is the latest in a series of steps OMB has taken in recent years to tighten government accounting practices. The agency has saved some $400 million over the past two years through simple administrative changes.

Separately, administration sources said President Carter intends to appoint a new "management improvement council" comprising officials and private citizens to consider other proposals for savings.

Among the suggestions the new panel is expected to consider are plans for obtaining discounts on air-fares for government-purchased tickets; using fixed contracts for Medicare services; and leasing public building space.