ITS NOT EXACTLY SURPRISING that Friday's three-hour meeting between administration officials and a Senate armed services subcommittee on the subject of a prospective newSALT agreement produced what Sen. Henry M. Jackson (D-Wash) politely called "differences of opinion," The last time Sen. Jackson and those Senate colleagues who more or less share his views were in generak accord with administration on this subject was much earlier this year when the administration sent a very tough proposal to Moscow with Secretary of State Cyrus Vance, causing the Russians to put on a great show of displeasure. The thing has been negotiated down-ward in stages since then, to the point where Moscow and Washington are giving indications of being on the edge of a mutually acceptable new agreement to limit offensive strategic nuclear weapons. What would have been surprising would have been a blissful and beaming Sen. Jackson stepping out of the hearing room to bless the outlines of the prospective accord. When the Soviets look to be placated and amenable to a deal, Mr. Jackson gets a certain suspicious expression - he wants to know why.

We've had our quarrels with Sen. Jakson from time to time on the substance of his complaints about the arms policies of several administrations. But that is not say thatwe find anything objectionable in his dogged insistence on fulfilling his congressional oversight responsibility in the arms-control field. On the contrary, we think that on the whole - and especially in relation to some of the more slovenly, snooze-now-holler-later overseers on the Hill - Mr. Jackson's hovering presence and his frequent interventions should be counted a good thing. This time around, although the tentative deal still seems to exist only in rough outline form, the subjects of hot controversy have emerged as these.

Whether the proposed limits on MIRV-ed land-based missiles in general and heavy Soviet missiles in particular are sufficient to diminish the threat to our own land-based missiles, which Sen. Jackson and others have worried about.

Whether the prospective arrangement to limit the production rate and deployment of the Soviet Backfire bomber can be vertified to the Senate's satisfaction.

Whether the limits we are likely to accept on the range and numbers of cruise missiles and the inhibitions against sharing the cruise technology with our allies are too harsh and restrictive.

Whether - and this is the big, overall question - the administration will have got the best deal it could have and whether this will be better than no deal at all.

Probably you can look forward to a great deal of controversy over these questions,as arcane as it will be noisy, in the weeks to come. Andif the past is any precedent, Mr. Jackson and some of his colleagues on the Armed Services Committee will present a series of stiff challanges to the administration to demonstrate the wisdom and safety of steps that seem on their face wise enough and safe enough to others. But that is what Mr. Jackson and his troublesome friends are there for, and ideally, with a little restraint and opemindedness all around, the debate and contention will improve theproduct. We find it encouraging the Secretary Vance has pledged to intensify consultations with Mr. Jackson and other interested senators as the negotiations with the Soviets now go into high gear. That is bound to make the administration's job more difficult and even at times, we have doubt, exasperating. But it also as good insurance as the administration can get that the accord it finally comes uo with will stand a strongchance of approval by theSenate.