Washington — It is likely to take more than a year and a half to negotiate a new strategic nuclear arms control agreement with the Soviet Union, according to the top US negotiator.
At the same time, Edward L. Rowny, chief negotiator to the talks with the Soviets (which begin in Geneva next Tuesday), sees tentative signs that the Soviets are giving serious consideration to President Reagan's proposals for major reductions in long-range nuclear weapons.
For one thing, he says, the Soviets have not rejected the Reagan proposals out of hand. And they have not been calling lately for ratification of the SALT II treaty of 1979, which the Reagan administration has described as ''fatally flawed.''
Rowny, a retired Army lieutenant general who resigned from the Carter administration negotiating team because he thought it was making too many concessions, says he doesn't think it will take as long to negotiate a new and ''improved'' treaty as it took to reach agreement on SALT II. The SALT II negotiations took 6 1/2 years.
In an hour-long interview with the Monitor shortly before his departure for Geneva, Rowny said he is not predicting a quick agreement. But he said he thinks the Geneva negotiations could move much more rapidly than the SALT II talks did, for at least two reasons:
* Much ground has already been covered in the SALT II negotiations. Parts of that agreement can serve as a basis for further progress.
''We don't have to reinvent the wheel,'' he said, indicating that the six-man US negotiating team that will sit down with the Soviets in Geneva wants to concentrate on improving on the ''flawed'' parts of SALT II.
* Both teams are expected to include officials who have considerable experience from previous arms control talks. Rowny noted that both he and Viktor Karpov, the chief Soviet negotiator, were at the SALT II talks ''from beginning to end.''
But he said a quick agreement was unlikely for several reasons. In fact, he said that it was ''extremely unlikely'' that he could come back from Geneva with a strategic arms reduction agreement before December 1983. To begin with, the Soviet negotiating style is slow and deliberate. Added to this, the United States is making far-reaching proposals that call for deeper cuts in the nuclear weaponry of both sides than were ever proposed before. Finally, he said, the Soviets are not likely to make a final agreement as long as they see a chance that West Europeans will refuse to go ahead with the agreed-upon deployment of new, medium-range American missiles in Europe. This deployment is scheduled to begin in December of 1983.
In Rowny's view, once the Soviets see that the US and its West European allies are serious about going ahead with that deployment, they will have greater incentive to negotiate a final agreement both on medium-range nuclear missiles and long-range missiles.
Talks with the Soviets on medium-range missiles began in Geneva last November. There has been no significant progress. In these intermediate nuclear force talks, the US has offered to withdraw plans for new missiles in Western Europe if the Soviets dismantle SS-20 missiles aimed at Western Europe. As Rowny sees it, progress in these negotiations will give a big boost to the talks on strategic, or long-range, nuclear missiles.
Rowny said the Reagan administration is devoting considerable attention to keeping its European allies informed as to its strategy in the talks on strategic nuclear missiles.
Reagan's proposals, outlined in a May speech at Eureka College in Illinois, call for both sides to cut the number of their long-range nuclear warheads by one-third. No more than half of the remaining warheads would be land-based. In the administration's view, this would reduce the threat from the ''most destabilizing'' of nuclear weapons, land-based intercontinental ballistic missiles.
The Soviets have criticized Reagan's proposals. On June 21, Foreign Minister Andrei A. Gromyko told reporters that the proposals were one-sided and would imply ''a very drastic change'' in favor of the US.