The abrupt resignation of Secretary of State Alexander M. Haig Jr. has added some new and unexpected elements to the U.S.-Soviet strategic arms reduction talks that open here tomorrow.

American officials say Haig's departure will not mean any shift in the opening U.S. proposals or positions. Those were set in final form Friday by President Reagan, officials say, at a lunch attended by Haig and the chief U.S. negotiator, retired Lt. Gen. Edward Rowny.

Rather, sources here and in Washington say, the impact of the resignation will be felt in peripheral yet potentially important ways.

The immediate impact, one official speculated, will probably be to make the Reagan administration appear "a little off balance" to the Soviet Union as the talks begin.

"It is certain to distract attention from what we are trying to do here," one official said.

Another said, "One of the things the Reagan administration needs is for the Soviets to perceive that we know what we are doing and have a coherent foreign policy." The Haig resignation and a vote in the House Foreign Affairs Committee last week supporting a nuclear freeze "both could not have come at a worse time," he said.

For now, therefore, Haig's resignation may make the Reagan administration seem even more of a puzzle to Moscow, in the view of some specialists. It and the nuclear freeze vote could lead the Soviets to adopt a wait-and-see approach at these talks. The Soviets favor a freeze, which the White House contends would formalize existing Soviet advantages in long-range missile power.

The longer-term impact of Haig's departure, the sources speculate, could come in determining what kind of an agreement, if any, emerges from these talks.

Within the administration, Haig was among those who argued at high level, with considerable success, for an American opening proposal that would make an agreement more negotiable in the Kremlin. He argued, for example, for concentrating in the initial phase of negotiations on trying to reach agreements lowering the number of missiles and warheads to equal levels and setting aside until a later phase the touchy question of trying to equalize overall missile lifting power.

The Soviet rocket forces have about 2 1/2 times the total lifting power of U.S. intercontinental missiles and the Pentagon and the Arms Control and Disarmament Agency both favored making that capacity one of the main measures for the first phase.

Reagan adopted Haig's approach in announcing the broad outlines of the U.S. proposal May 9. Shortly afterward, Haig also said he expected that after the first phase--involving numbers of missiles and warheads--was finished, an agreement would be concluded before going on to the second phase, dealing with total carrying capacity of the missiles.

But Haig never again repeated that formula publicly. Since then Rowny and others, while leaving the door open to a possible first-phase agreement, have stressed that they envisage only one treaty and that both phases would be negotiated as a continuing process.

Thus, the harder-line Pentagon view may come to prevail--a prospect Moscow undoubtedly is now studying.

Secretary of State-designate George P. Shultz has no experience in the arcane business of controlling strategic nuclear weapons. How much housecleaning is done by Shultz at state could also affect how much of Haig's views survive.

On the other hand, there is the possibility that the departure of Haig could clarify Soviet thinking. It means there is nobody of Cabinet rank in the administration or in the White House who is generally considered as a moderate on the issue of arms balance with Moscow. The Soviets would know they are up against a thoroughly hard-line team.

Whether this will help or hurt chances for an agreement is unclear. But some government specialists say that while the administration has done some puzzling things, they think the Soviets understand Reagan's tough rhetoric and have been impressed with his ability thus far to keep the defense budget high despite his other economic problems.

Rowny, a veteran of more than six years on previous U.S. delegations to the Strategic Arms Limitation Talks (SALT) between 1973 and 1979, was the representative of the joint chiefs of staff for the SALT II agreement signed by Presidents Carter and Brezhnev in June 1979, but never ratified by the United States.

Rowny resigned from the Army and the delegation in 1979 and became a critic of the treaty contending that the administration was negotiating something that would leave the United States in an inferior position.

Rowny, 65, is a soldier-scholar who speaks "serviceable" Russian.

Under Rowny are two experienced officials. His deputy is Ambassador James E. Goodby, a former senior State Department specialist in political-military affairs. The other is Jack W. Mendelsohn, who was a member of the SALT II delegation and is an official of the arms control agency.

The least experienced key members are both from the Pentagon. Representing the defense secretary is a lawyer, Michael H. Mobbs, who has no experience in arms control but speaks Russian and has experience in commercial negotiations with the Soviets.

The new joint chiefs representative is Rear Adm. William A. Williams, who also had had no arms control experience other than the six months since the negotiating team was formed.

The Soviet delegation chief, Viktor P. Karpov, is a veteran member of the SALT I and SALT II delegations who knows Rowny well. His deputy, Maj. Gen. V.P. Starodubov from the Defense Ministry, is also an experienced SALT veteran.

A Foreign Ministry representative, A.A. Obukhov, also a veteran of SALT negotiations, speaks English well and studied at the University of Chicago.

The Soviets also have some first-timers, including Col. V.P. Mironov of the Defense Ministry and K.G. Osadchief from the civilan Council of Ministers.

The executive secretaries of the delegations are V.G. Alexandrov for the Soviets and Donald C. Tice for the United States.