The Senate will approve the new U.S.-Soviet nuclear arms treaty next year unless "unexpected flaws" are discovered, Senate Democratic Whip Alan Cranston (D-Calif.) predicted yesterday on the basis of preliminary counts indicating that no more than 10 senators now appear likely to oppose the pact.

Cranston, a leading pro-treaty strategist, said there also appear to be enough votes to fend off crippling amendments, but he cautioned that "ingenious minds are at work" drafting potentially troublesome proposals.

Cranston's assessment was the latest in increasingly optimistic forecasts for the two-thirds vote necessary for Senate approval of the treaty signed here Dec. 8 by President Reagan and Soviet leader Mikhail Gorbachev to eliminate medium- and shorter-range nuclear weapons. At their summit, the two leaders announced plans for Reagan to visit Moscow in June.

Last week, Senate Minority Leader Robert J. Dole (R-Kan.) endorsed the Intermediate-Range Nuclear Forces (INF) Treaty and predicted its approval in a move seen as bolstering support for the pact among GOP conservatives who have voiced the strongest objections. Senior Republican leaders in the Senate now unanimously support the treaty, and foes of the pact concede that approval now seems a foregone conclusion.

But Cranston's observations at an end-of-the-session news conference also reflected lingering concern over the possibility of "killer amendments" that could be adopted by majority vote, requiring renegotiation of the accord along lines that the Soviets would find objectionable.

Cranston said these could come in the areas of verification, conventional-force levels, enforcement of past treaties and restrictions on negotiation of future agreements dealing with reduction of strategic nuclear weapons. A 1979 Strategic Arms Limitation Treaty remains unratified, having never come to a vote in the Senate.

He said he sees no change for fatal tampering with the treaty on issues that are not directly related to it, such as demands for Soviet withdrawal from Afghanistan as a condition for implementation of the pact.

To head off attempts to kill the treaty by indirect means, Cranston said opponents are working on

ways to satisfy senators' concerns without jeopardizing the treaty itself.

Dole, in an op-ed article

scheduled to appear in today's editions of the Des Moines Register in Iowa, where he is campaigning for the Republican presidential nomination, also expressed concern about "killer amendments" and pledged to help lead the fight to defeat them.

Dole said there may be one or more "Dole initiatives," which he said would be backed by the president, to address senators' concerns over verification, compliance and the imbalance of conventional military forces in Europe without jeopardizing the treaty.

Elaborating on remarks at his news conference, Cranston said that he counts "less than 10" outright opponents to the treaty, although the number could change depending on amendments and reservations as the treaty makes its way through the Senate.

"I think there are now enough votes to assure approval," he said, adding that "there are very few people willing to take it {the treaty} on directly."

As for blocking crippling amendments, he said, he is "reasonably hopeful . . . but not totally confident" of success.

Cranston's comments came as treaty proponents scaled a preliminary procedural hurdle in winning unanimous Senate consent necessary for the Foreign Relations Committee to hold hearings on the accord while the Senate is in session. An unnamed Republican had been holding up the agreement, prompting Foreign Relations Committee Chairman Claiborne Pell (D-R.I.) to threaten to begin the hearings a week before the Senate returns Jan. 25 to avoid disrupting the hearing schedule.

Senate leaders credited Sen. Jesse Helms (R-N.C.), ranking Republican on the committee and a leading critic of the treaty, with resolving the dispute.

Another possible wrinkle emerged in a letter to Reagan from Sen. Pete Wilson (R-Calif.), who has not endorsed the treaty and has a home-state problem with the verification provisions.

While the State Department has said only one building of a General Dynamics Corp. plant in San Diego would be subject to verification inspections, Wilson said, the Pentagon has told his staff that all buildings at the plant would be open to Soviet inspection.

These include buildings that General Dynamics would use for construction of the rail-mounted MX missile launcher if the company wins the contract. But the MX is not covered by the treaty and hence off-limits to Soviet inspectors, a problem that could preclude General Dynamics from winning the MX launcher contract, Wilson complained. The issue is "not trivial," said Wilson, suggesting that the issue may have to be resolved with the Soviets if the Pentagon interpretation is correct.