What tipped the presidential decision toward preparing ground for a summit meeting with Yuri Andropov next year - perhaps early next year - was something beyond the main objective of pursuing peace:
President Reagan is pictured as having bought the rationale that an easing of the arms race is necessary if he is substantially to reduce the massive budget deficit.
Reagan political strategists are troubled by that deficit. They have brought their anxieties to the attention of the President, pointing out how damaging a possible dip in the economy could be to his administration and how necessary it is that he find ways to reduce expenditures.
These strategists note that the impact of arms-control-related relief on the budget could not come before late in Reagan's first term at the earliest. But their view is that the President will run and be reelected - and that the budget problem will still be there to be addressed.
The summit, as now envisioned, would not have arms talks as the patent objective. Instead, the Reagan camp would put economic issues, especially East-West trade, at the top of the agenda.
But the President would be expected to lean heavily on his experience as a negotiator - as a union chief, as a governor, and as a successful bargainer with Congress during his first two years in office - to try to nail down an ending or a slowing of the nuclear arms race.
With an agreement easing East-West tensions in hand, it is thought the President could pull this off, and then would be positioned to propose big cuts in defense spending to bring the deficit down to proportions no longer causing anxieties in the business community.
The new Reagan position of being ''favorably disposed'' to a summit is a change in direction. Previously the President had indicated that only if an arms reduction pact were in place in advance of such a meeting would he be willing to sit down with Andropov. Now, it seems, he would be willing to discuss arms without tangible results being guaranteed.
This new ''disposition'' to engage in summit diplomacy underscores the following presidential positions:
* In no way is Mr. Reagan giving in to pressure from Democrats who insist he must cut proposed defense increases in order to deal with the deficit.
That defense buildup is a Reagan commitment that he gave to the voters. He intends to fulfill it - certainly to the point of achieving an arms build-down pact with the Soviets. Even then he would insist on keeping the nation defensively very strong, approximating a parity with the Soviets.
Of course the Reagan view continues to be that only with this buildup in defense will he be able to bring Andropov to the summit; that with the MX missile in the US arsenal, plus the Pershing missile that is soon to be deployed in Western Europe, Andropov will be quite willing to sit down and talk about putting a mutual restraint on the nuclear arms buildup.
* The President retains his view that the deficit could be reduced sufficiently if Congress would be willing to cut more deeply into social programs.
But he has become convinced that he can make little headway here, argue as he may that there is ample fat to be removed, particularly in entitlements and automatic cost-of-living increases that Congresses of the past, prodded by President Johnson, put into effect.
* But the President is still concerned about a recovery which his economic advisers have told him is of tentative nature and might lose its steam by election time next year.
It is within this context that the President is giving thought to a summit as a means of making adjustments in defense spending and the budget deficit, and thus putting business confidence back on a firm footing.