Those involved with legislation that will provide for the forthcoming Puerto Rican status referendum will welcome The Post's July 13 editorial "Taking Puerto Rico Seriously." The referendum will, of course, present the choice of commonwealth, statehood or independence.

The Post writes: "The status issue is important in its own right. Puerto Ricans are U.S. citizens but have neither all the rights nor all the obligations of citizenship. The threshold question for them as for the U.S. public and Congress is whether that incomplete status is fair."

I wonder if these are quite the words The Post wants. The present commonwealth status dates from the time of Luis Munoz Marin, who in 1948 became the first elected governor of Puerto Rico. Puerto Ricans drafted the present constitution, Congress approved. As best I understand -- here I am following Arnold Leibowitz in his authoritative "Defining Status" -- this was seen as creating more than local self-government. To the contrary, it was contended that "a new legal entity was created, with a unique status in American law: the commonwealth, a status which is an internationally recognized non-colonial status."

The United States promptly informed the United Nations and requested that Puerto Rico be removed from the list of Non-Self-Governing Territories compiled by the General Assembly. The General Assembly thereafter passed Resolution 748(viii) (1953), which recognized that commonwealth had "achieved a new constitutional status" and that the people of Puerto Rico now had "attributes of political sovereignty which clearly identify the status ... as that of an autonomous political entity." As U.N. ambassador in the mid-'70s, I had more than one occasion to refer to this resolution.

Mr. Leibowitz writes: "The Popular Democratic Party of Puerto Rico created commonwealth status as a permanent status equal in dignity to statehood and independence with a political validity on the island." (The PDP was, of course, Mr. Munoz's party, and is the party of Gov. Rafael Hernandez Colon.)

In this view, commonwealth is not an "incomplete status." To ask whether it is "fair" is to adopt the language of those who think it is not desirable, opting instead for statehood. This, of course, is the view of the New Progressive Party, and its leader, former governor Carlos Romero-Barcelo. It would be my thought that, as much as possible, Congress ought to be neutral in the matter.

This takes us to the question of whether the forthcoming referendum should set forth the details of any of the choices. Again, it is the commonwealth position that is the sensitive one. The terms of independence and statehood are clear. Some transitional arrangements can be stipulated, but it can't much matter. In a very short space of time, statehood will mean statehood, period. Independence will mean independence.

On the other hand, the PDP is asking for "enhanced commonwealth" status to be stipulated in the referendum. This mostly comes down to greater social welfare benefits. These are not small matters in the lives of Puerto Ricans. Consider the Supplemental Security Income program. The current benefit in the commonwealth is about $32 a month for the needy blind, disabled and aged. Under statehood, these benefits automatically increase to $386. Is Congress willing to provide the same benefit under commonwealth? Half? No change? I would have thought these are matters that want spelling out, if an informed choice is to be made. But perhaps I am wrong.

As for the question of a two-stage process whereby Congress first sets up the referendum, with or without details, and thereafter ratifies the results, I think The Post is right. The Senate should follow the House in this regard. DANIEL P. MOYNIHAN U.S. Senator (D-N.Y.) New York