A outline on the cover of Sunday's Business and Finance Section incorrectly identified Rep. Joseph P. Addabbo (D-N.Y.). He is chairman of the defense subcommittee of the House Appropriations Committee.

When former President Richard M. Nixon began impounding appropriations money in 1973 to try to force Congress to stay within his budget, he unexpectedly set off a major reform.

Fearful of losing their power over the purse strings, the lawmakers created a new congressional budget process, complete with mandatory tax and spending ceilings and a new Capitol Hill budget agency to provide staff backup.

When the new procedures went into effect in early 1975, the old helter-skelter congressional budget making was a thing of the past.By early 1977, the procedures were being hailed as an unqualified success.

Today, however, the 4 1/2-year-old congressional budget process is heading for a new crossroads that some critics say could prove as difficult to handle as Nixon's original challenge to Congress.

The question: Can the still-fledgling process cope with President Carter's new fiscal 1980 spending plans -- due out tomorrow -- and their expected new pressures for sharp cutbacks in old-line Democratic social programs?

Most onlookers believe the lawmakers -- and the process -- eventually will come through. But experts agree that the way the issue is handled could make -- or cripple -- the new budget procedure for several years to come.

"This is the testing time for the budget process," says Alice M. Rivlin, director of the Congressional Budget Office, Congress' new budgetary analysis arm. "The pressures will be greater than at any time since the start."

The consensus is that the budget process has done well enough as far as it has gone -- beyond its original sponsors' wildest dreams -- in reforming Congress' handling of federal budget and spending problems: It has created order out of chaos and has imposed a binding ceiling.

But experts say a good many more changes are needed if the procedure really is to make a long-term difference in how well Congress gets a handle on the budget. The new budget procedure has only made a beginning -- not accomplished a thorough reform.

Moreover, since the process was established, the road has been a relatively easy one. The mostly Democratic congresses have had only to face either a GOP president whose proposals could be ignored or a Democrat who wanted to boost spending.

This time, however, the president proposing the cutbacks is a Democrat, and the political pressures conflict: Voters want to see the deficit cut, but special-interest groups are fighting to avoid cutbacks in their programs.

Analysts say that as a result, although the lawmakers easily will endorse the president's overall budget targets, Congress is headed for bitter internal fights over where to make the cuts needed to reach those goals.

Moreover, Congress' own economic forecasts are expected to predict a higher unemployment rate than the Carter administration, making it more difficult for Congress to meet Carter's target -- and straining the budget process further.

If the process is relatively smooth, it could heighten the power of the House and Senate budget committees and pave the way for further "reforms" in the congressional budget-making procedure in coming years.

But if the system buckles too much under these pressures, it could leave the budget process as little more than it is right now: a way to tidy up congressional budget making, but not really overhaul it.

Budget experts offer this assessment of the budget process so far:

By far its most important achievement has been to force the lawmakers for the first time to consider individual spending and tax decisions in the context of an overall congressional budget target rather than as isolated votes that have no relationship to any others.

Before Congress adopted that discipline, the lawmakers were able to vote for all their pet programs without having to face cutbacks in other areas. The result was fiscal chaos: There rarely was a majority to force a cut in any one area, so spending levels simply soared.

Today, largely because of the new budget process, Congress now is forced to consider the budget as a single unit before deciding on individual spending bills. Moreover, the procedure has become a vehicle for Congress to debate and set national economic policy -- something the lawmakers never did before.

The new machinery also brought Congress its first serious budget-analysis and -tracking operation, in the form of the Congressional Budget Office -- a meticulously nonpartisan and highly proficient agency that provides economic and budgetary backup for both houses.

Although some of the CBO's peripheral work is regarded as spotty, the agency is considered thorough -- and as skilled as Carter's own budget makers -- on basic economic and budgetary computations. The result: Congress now has the wherewithal to reach its own independent conclusions.

Although the new procedures have brought substantial order to congressional budget making in recent years, it is not clear whether they have resulted in any substantial "savings" from what Congress would have appropriated under the previous system.

Sen. Edmund S. Muskie (D-Me.), chairman of the Senate Budget Committee, once claimed the process "saved" Congress some $15 billion, but serious analysts suggest the figure is at most only a few billion dollars. Some even say the process has merely brought order to the procedure, not resulted in cutbacks.

The few cutbacks the process has made have been almost exclusively in proposals for increasing previous spending levels. The system rarely has dealt at all with trimming existing entitlement programs, the so-called "uncontrollables" that critics say lie at the heart of the budget problem.

An often-quoted example is the controversial "impact aid" program for public schools in areas where there are large numbers of federal workers. Although several presidents have tried to reduce the plan drastically, Congress persits in extending it. The budget process has made no difference.

Although the budget process has succeeded in limiting total spending levels each year, it still has been virtually unable to get a grip on tax-cut legislation, which affects the overall deficit figure as much as outlay levels do.

The new process has run into a few procedural snags. The tight May 15 deadline for approval of the initial budget targets often has conflicted with the timetable for the two houses' legislative committees to finish their authorizing bills.Some housekeeping changes seem in order.

By far the most serious shortcoming has been the inability of congressional budget makers to set binding targets for future-year spending, as well as that for the upcoming fiscal year -- a step critics say is necessary before the lawmakers really can get a handle on the budget.