Vice President Bush today rejected contentions that a "point of no return" will be passed unless agreement can be reached with the Soviet Union to eliminate new U.S. medium-range nuclear missiles in western Europe before they are deployed beginning in December.

"My answer to that," Bush said at a press conference here, "is that what goes in can come out," meaning the United States would be willing to continue negotiating for eventual withdrawals on both sides.

American and European officials said they were pleased to hear Bush make this point.

Soviet Foreign Minister Andrei Gromyko recently told West Germans that starting deployment of the new Pershing II and cruise missiles could create "a years-long confrontation for the whole world." Other Soviet leaders have hinted they might break off the arms reduction talks or add to the 600 medium-range Soviet missiles already targeted on western Europe.

Bush also came closer than before to acknowledging indirectly that Washington might accept an "interim" alternative to President Reagan's "zero-zero" proposal that the Soviets dismantle all of their missiles in return for cancellation of U.S. missile deployment.

Asked about the possibility of an intermediate step in which the two sides would be allowed an equal smaller number of missiles, Bush replied, "If a sensible proposal is brought by the Soviets that fits that description, so be it."

The administration has stayed away from language like "interim," "compromise" or "alternative" to impress Moscow that the zero-zero plan is best and that the NATO allies are unified behind it. Bush today reaffirmed his dedication to the zero-zero plan and, throughout his European tour, allied leaders have said it would be the best solution.

But the initially favorable European reaction when the Reagan plan was announced in November, 1981, has eroded. Allied leaders are now wondering aloud about a compromise.

In recent days, British Prime Minister Margaret Thatcher told reporters that "if you can't get" the zero-zero solution, then you "must have a balanced number of forces, the lower the better."

Both Thatcher and West German Chancellor Helmut Kohl have pointed to the original 1979 NATO decision to deploy new missiles if no arms control agreement is reached, which suggests "limitations" negotiated in a step-by-step approach.

Authoritative sources said the crucial choice facing Washington when Bush returns next week will be whether to make another proposal to the Soviets.

All allied leaders are insisting that any compromise must leave NATO with enough missiles to balance those aimed at western Europe by the Soviets.

Some of these leaders are said to be pressing for a U.S. decision on a new initiative within the next month or two because they fear that support for the zero option is fading quickly. Others are suggesting that the alliance wait at least until after the March 6 West German elections.

But some senior NATO officials say the Soviets are not likely to accept a compromise that would allow any new U.S. missiles to be deployed or that would undercut Soviet supporters in the European peace movement.

Even more complicating is the Pershing II missile. The Soviets want most to stop its deployment, because from bases in West Germany it could strike targets deep inside Russia with virtually no warning. But if the planned deployment of 108 Pershings in West Germany is dropped in a compromise agreement, political problems could erupt elsewhere in western Europe.

New missiles are to deployed at the same time in West Germany, Italy and England, beginning in December, so no country stands alone. But only West Germany gets Pershings; Italy and Britain get cruise missiles.

West Germany also is to get cruise missiles, but not until 1985. So Britain and Italy would be the only countries deploying missiles this December, and political pressure on those two nations, both from within and from the Kremlin, would greatly increase.

Moreover, taking West Germany off the front line in carrying out the NATO decision would make it more difficult ever to deploy missiles there. So the NATO allies, including Kohl, according to officials, have been urging Washington to retain the same mixture of missiles in any compromise agreement to scale down their numbers.