Amercian officals yesterday expressed guarded optimism that meetings begining today in Geneva between Secretary of State Cyrus Vance and Soviet Foreign Minister Andrei Gromyko will remove the last important obstacles to a new strategic arms agreement.

U.S. sources indicated that the meetings might go beyond their schedulled two days a prospect also raised by Gromyko in an airport statement when he left Moscow yesterday.

Arriving at Geneva, Gromyko told reporters it would be "too much to hope for" a final accord at these meetings. This appeared, however, to be reference to completion of a full agreement, and U.S. analysts in Washington expressed optimism that the Soviet side is ready to resolve the few remaining sticking points in the SALT negotiations.

Some high-ranking Americans involved in the talks were nevertheless pessimistic that a final agreement in principle can be reached at these meetings. White House planners discussed ways to handle the outcome either way.

"It's fifty-fifty," one senior-offical said. Others were more hopeful.

In a formal arrival statement, Gromyko said he hoped the meeting with Vance "will substantially advance us" toward a final agreement. Tuesday night in Moscaow, Gromyko said in a toast at a diplomatic dinner that he hoped the two superpowers would find "mutually acceptable solutions"in Geneva to outstanding SALTissues.

Some American analysts argue that the Soviets will prove forthcoming at these meetings in reaction to President Carter's surprise announcement last Friday that the United States and China will open full diplomatic relations Jan 1.

According to this view, the Soviets will be anxious to shore up their relationship with the United States to protect their own interests and to remind the United States of the benefits of Soviet-Amercian cooperation. The Soviets seemed to pursue a similar policy in 1971-72 after former president Richard Nixon announced his opening to China and made his first trip there. Several months after the trip the first SALT agreements were signed in Moscow.

Other analysts argue that the warming of Sino-American relations may give Moscow pause and slow down the Salt II process.

Adherents of the first view took heart from the friendly message that Soviet leader Leonid brezhnev sent to Carter this week, praising the decision to recognized China as a peaceful act. Carter revealed the contents of this message Tuesday night.

Some analysts said that message showed how much the Soviets want to maintain their relationship with the United States in the face of a more pragmatic, outward-looking Chinese foreign policy.

Resolution of outstanding SALT issued at these Geneva talks would make possible a Soviet-Amercian summit meeting in Washington early next year.

The administration reportedly favors a January date for such a meeting, but the Soviets prefer February.

The Soviet may feel tha tBrehnev should come to the United States after the visit of Teng Hsiao-ping, scheduled to begin Jan 29.

Three substantive issues remain unresolved in the SALT talks.

Putting into code the electronic signals sent back to earth by Soviet missiles on test flights. The United States regards this as a deliberate attempt to interfere with American ability to monitor a SALT pact and insists that the Soviets promise not to do it.

The number of cruise missiles-unmanned deones designated to hit targets with uncanny accuracy-that the United State will be able to mount on B52s or other bombers under the agreement. The United States is said to demand aat least 30 per plane, but the Soviet have suggested 20.

A letter of understanding the Soviet will provide in addition to the fromal agreements accepting certain restrictions on production and deploument of a mediim to long-range bomber called the Backfire. The United States seeks assurance that this plane will not be produced in larger quantities than at present and that it will be based in ways that would make it more difficult to use in an attack against the United States