Senate consideration of the strategic arms limitation treaty (SALT II ), once anticipated as the focus of a great national debate, begins in the Foreign Relations Committe today in the shadow of national preoccupation with other issues.

Secretary of State Cyrus R. Vance and Defense Secretary Harold Brown will be the first witnesses today, initiating an intense series of hearings that will last for a month and resume again in the fall after the August recess.

Until energy problems deflected both public and governmental attention, the hearings promised to be dramatic and the object of intense interest, now, a senior administration official noted over the weekend, "SALT is likely to be only the second or third story on the evening news show Monday night."

The reorganized Foreign Relations Committe under Sen. Frank Church (D-Idaho) hopes to enhance its stature by conducting a thorough and balanced set of hearings. However, the committe's preparations have been hampered by some disorganization, tense relationships within the membership and staff and occasional strains between the committee and the executive branch.

At the end of last week, senators on the committe said they still did not have a list of witnesses for the SALT II hearings after the first two weeks.

According to colleagues and the committe staff, Church has been distracted in recent months by political problems in Idaho, where he faces a serious challenge in next year's campaign. As recently as 10 days ago, Church had not yet fully familiarized himself with the contents of SALT II.

The committe plans hearings on the broad political context for SALT II as details. The senators will hear from administration officials, hawkish and dovish critics of SALT II and many others.

The new staff director, William Bader, has retained outside consultants to prepare for the hearings. The consultants have drawn up briefing papers covering most of the controversial aspects of SALT II.

Public telivision will broadcast the hearings live, as will National Public Radio.

Two weeks from today, the Senate Armed Services Committee plans to begin its hearings, calling many of the same witnesses who will appear at Foreign Relations. Armed Services is considered more hostile to SALT II, but the administration hopes that its friends on the committee -- particularly John Culver (D-Iowa) and Gary Hart (D-Colo.) -- will prove to be effective interrogators and articulate defenders of the treaty.

This year's substantially altered membership of Foreign Relations includes several senators who are expected to question administrative witnesses regorously and critically, among them Jesse Helms (R-N.C.) and Richard G. Lugar (R.-Ind.).

A high point of the committee's hearings could come at month's end when Henry A. Kissinger is expected to testify. Former Secretary of State Kissinger, who has been avidly courted by Vance and other administration officials since the SALT II agreement was reached, could play a crucial role in shaping the views of moderate Republicans whose support is vital if SALT II is to win two-thirds Senate approval.

This week the committe will spend three days questioning administration officials, and one day listering to critics of SALT II. One of them -- scheduled to testify Thursday -- is recently retired Lt. Gen. Edward L. Rowney, who was the Joint Chief of Staff representatives on the SALT II delegation. CAPTION: Pictures 1 and 2, SECRETARY OF STATE VANCE, SECRETARY OF DEFENSE BROWN . . . to testify on arms treaty before Senate Foreign Relations Committe today. AP