The United States and the Soviet Union have reached "rough equivalence" in overall military power but each side has special advantages that must be weighed in any new war planning, Defense Secretary Harold Brown said at a closed White House meeting yesterday on the global balance of power.

Brown, in chairing the meeting sponsored by the National Security Council, cited the Soviet Union's proximity to Iran and other oil-producing nations in the Persian Gulf as one of Russia's stragetic advantages that must be given significant weight in making a net assessment of power for President Carter.

Brown's remarks, administration sources said, came during the second meeting on Presidential Review Memorandum 10. Prof. Samuel Huntington of Havard was the principal author of a net assessment report discussed at the first PRM-10 meeting at the White House on Thursday.

In citing the Soviet advantages in being close to Persian Gulf oil producters, Brown was reflecting a deep concern felt by U.S. Navy leaders that in a crisis the Soviet Union could shut off much of the North Atlantic Treaty Organization's oil supply by controlling a few straits used by tankers.

Brown went to the White House yesterday morning to chair a meeting on a draft of the "force posture" section of PRM-10. It outlines various possible military strategies and how many American troops and weapons would be needed to implement them.

The net assessment and force posture papers together run over 500 pages, sources said yesterday. They add up to a general overview which the National Security Council may eventually reduce to specific recommendations.

Interagency task forces studied these five broad contingencies and then listed the forces that would be needed to handle them: (1) a Warsaw needed to handle them: (1) a Warsaw Pack attack on NATO in Central Europe: (2) an East-West war outside (4) "national" wars like Vietnam, and (5) all-out nuclear war with the Soviet Union.

Agencies represented at yesterday morning's session on force posture included the State and Defense departments and the Arms Control and Disarmament Agency.

Jerrold Schecter, press officer for the National Security Council, refused when asked yesterday to name the government executives who attended the meeting, declaring it an internal matter.

A third meeting is scheduled for Wednesday.

Officials who had been briefed on the force posture statement said it contained no surprises, repeating the oft-stated need to continue beefing up NATO forces to combat the Warsaw Pact buildup. The Soviet-Warsaw Pact superiority in armor was underlined anew, sources said, as was the growing number of Soviet tactical nuclear weapons.

Since becoming defense secretary, Brown has taken a far less alarmist view of the Soviet military buildup than did his Pentagon predecessor, Donald H. Rumsfeld.

"Generally speaking," said Brown in a recent statement to Congress, "there is no reason for immediate or grave alarm about our ability to deter major military actions by the Soviet Union. A comparison of United States with Soviet investments during the past 20 years will show that, cumulatively, we have made as large an effort as the Soviets.

"However," Brown continued, "a major part of the U.S. effort came during the first 10 years, while the most significant Soviet investments have been made during the past decade. We have probably lived off our earlier investments longer than we should. We have some catching up to do."

Brown, in a recent interview with The Washington Post, predicted that the first responses to PRM 10 would fail to push thinking about military force out of well-worn ruts. But he that eventually would provoke fresh thinking on long-standing problems.

"I don't think we're limited to the first time around," Brown said. "We are going to ask some very different questions about how things might be done very differently."

However, he warned that "this is not going to be easy, because those of us who have been in the defense area a long time tend to get into a rut. It's not easy to get out."