The item veto: an idea whose time shouldn't come

President Reagan and the Republican Platform adopted in Dallas urge amending the Constitution to strengthen the president's veto power. The Constitution now provides a president may veto bills coming to the White House for signature. This measure would permit a president to veto or in effect delete any item or subsection of an appropriations bill passed by Congress.

The Constitution currently provides that a presidential veto may be overridden by a two-thirds vote of those present and voting in each house of Congress, assuming a quorum is present in each. Most proposed item veto amendments call for a similar process by which Congress could override a presidential item veto.

Reagan and his New Right friends who wrote the Republican Platform are not alone. Seven or eight presidents have called for this change - including Franklin D. Roosevelt, Harry Truman, and Dwight Eisenhower. According to polls, a majority of Americans favor it.

Why change the Constitution? Their arguments: First, it might reduce the pork-barrel extravagance in congressional appropriations. Congress often attaches wasteful items to critically important bills in an effort to make it more difficult for a president to use the veto power. ''Logrolling and packaging good and bad projects and programs into a single omnibus bill,'' says Sen. Alan J. Dixon (D) of Illinois, ''has become a way of life.''

Second, the late passage of crucial appropriations bills near or even beyond the end of the fiscal year usually forces a president to sign a bill that contains objectionable or inflationary provisions, for a regular general veto of the whole measure - which is the only kind of veto a president is now permitted - would lead to the shutdown of several of the departments due to lack of funds.

Third, it is sometimes said that the president's veto power is now almost worthless. The intent of the framers, it is suggested, has been subverted. Congress almost routinely tags on programs and spending they know he will not like with various essential programs and projects the president dearly wants approved. What is a president to do? He can send the whole package back, but there is the risk his own programs might not make it through again.

Fourth, many fiscal conservatives are now saying this would be a major weapon for presidents to use to reduce the soaring national budgetary deficits.

Plainly, these are intriguing reasons and they explain the popularity of the issue. And plainly the item veto, if only occasionally and prudently used, could be a tool to trim some excessive or wasteful spending by Congress. There are, however, persuasive reasons for rejecting this proposed amendment to the Constitution.

Perhaps the strongest reason against this proposal is that it would be a major transfer of power from the Congress to the presidency - a grant of authority that would diminish the capacity of Congress to function as a separate and equal branch of government. ''If Congress were ready to surrender its legislative powers,'' says Sen. Lawton Chiles (D) of Florida, ''this would be a good way to do it.'' If the president were granted this power, the White House and budget aides to the president would be able to ''edit'' and rewrite on an item-by-item, line-by-line basis legislation passed by Congress. The president already is a dominant force in the legislative process. Not only would Congress yield its legislative powers in a dramatic way, but it would also significantly diminish its power of the purse.

The question really revolves around whether you want one person to have all that power. Conservatives might like it when Reagan occupies the White House, but what if Gary Hart or Mario Cuomo were there? Decisions are now made through give and take between the branches, a system of transactions and compromise that form the legislative process - a pretty good balance.

Giving presidents the item veto may also lead to undesirable levels of pressure tactics and political retribution. Presidents or presidential aides who lobby the Congress might be encouraged to intimidate members of Congress who are not going along with the president by checking through all the computer printouts indicating present or pending federal projects in a member's district. ''We have all witnessed the power of the president when he lobbies Congress by telephone,'' writes Sen. Mark O. Hatfield (R) of Oregon. ''It doesn't take much imagination to consider how much more persuasive he would be if his words were buttressed with a veto stamp over individual projects and activities within our districts.''

The item veto, if approved, could make Congress even more irresponsible. Now, one house of Congress sometimes tacks on a measure with the understanding that the other house will cut the project out. With the item veto, Congress might be unrestrained in tacking on countless spending projects, thinking that the president would delete them with the item veto. ''There is more,'' says political scientist James Sundquist. ''And would the president really do the dirty work, or would he be under the same pressures that the Congress yielded to?''

That most of the states grant this authority to governors is not a persuasive reason to give it to presidents. Most state legislatures are part-time institutions, and they often pass only a few lump-sum appropriations bills near the end of their sessions. A governor would have to veto or accept the entire bill. But that is not the case with Congress. Congress is now a full-time institution, and there are over a thousand items in the national budget - a document to which the president and his budget director contribute by proposing items and guidelines.

Finally, a president already has a variety of ways he can help balance the budget and reduce deficit spending. A president now has the initiating power of suggesting the proposed fiscal year budget that Congress works on. A president who truly wanted a balanced budget should propose one in the first place. A president who disliked major spending projects can and should use the existing general veto regularly. Reagan has used that very sparingly. Or, under the 1974 Budget and Impoundment Control Act, a president can defer what he deems unnecessary spending until the end of the fiscal year.

Reagan and other supporters of the item veto do us a disservice when they do not frankly acknowledge that two of the three or four leading causes of our huge deficits have been brought about by Reagan policies - major tax cuts and major defense spending increases.