The Senate scheduled fast action yesterday on the prospective U.S.-Soviet treaty to eliminate short- and intermediate-range nuclear-armed missiles in Europe as the Foreign Relations Committee set hearings to begin Jan. 19, the day Congress plans to return from its Christmas recess.

Under the schedule for the treaty, the INF agreement is expected to reach the Senate floor for a ratification vote by early March. The schedule was disclosed amid signs that conservative Republican opposition to the pact may not be as strong as it once appeared.

But Democrats as well as Republicans indicated that the White House is unlikely to get its wish for ratification of the treaty without reservation or amendment, and Majority Leader Robert C. Byrd (D-W.Va.) cautioned against Senate submission to a "razzle-dazzle selling job from this unlikely political duo" of President Reagan and Soviet leader Mikhail Gorbachev.

Unless there is a "demonstrated level of confidence" in verification procedures and other provisions for implementing the treaty, Byrd warned, the prospects for a broader strategic arms pact could be "fatally damaged."

While some ardent conservatives are still voicing strong objections, others such as Orrin G. Hatch (R-Utah), Don Nickles (R-Okla.) and Charles E. Grassley (R-Iowa) have indicated at least qualified support for the agreement that Reagan and Gorbachev are scheduled to sign here next week.

Several cited the pact's reported verification requirements as a major reason for supporting the treaty, saying they are more stringent than had been expected. "If {the treaty} comes out as it looks it will, it will be a major breakthrough," Hatch said. "I still have some questions, but the thrust of it is very positive," Nickles said. Grassley said he was concerned about compliance guarantees but added, "The more you hear about the intent, the more you like the treaty."

Sen. Thad Cochran (R-Miss.), secretary of the Senate Republican Conference, interpreted these and other indications of support as a "very good sign" that a "comfortable majority of Republicans" will join most Democrats in ratifying the treaty.

But Sen. Jesse Helms (R-N.C.) and others who have raised especially strong objections to the treaty dismissed suggestions that conservative opposition may be crumbling. "There's still a lot of muttering and hollering," he said.

Rather than concentrating on defeating the treaty, Sen. Dan Quayle (R-Ind.) suggested conservatives will try to use their votes to win administration support for reservations because the White House wants to win ratification by a large margin and "they will not get it unless they deal with us," according to Quayle.

Minority Leader Robert J. Dole (R-Kan.) said a new charge by the administration Tuesday that the Soviets are violating existing treaty requirements points up the need for "a strong compliance regime . . . written in language that is crystal clear." While he has endorsed neither the treaty nor specific reservations, he said the administration report indicates "no deal with the Soviets is worth much unless it is 100 percent verifiable."

Majority Whip Alan Cranston (D-Calif.), who is expected to play a key role in ratification, agreed that the critical battles are likely to occur over reservations rather than ratification. He predicted the most contentious fights would occur over such issues as verification, compliance standards and the continued deployment of Soviet troops in Afghanistan.

Rejecting White House assertions that Reagan will insist on keeping the treaty free of reservations and amendments, Cranston said it is "not realistic" to assume that the Senate will do nothing but ratify the pact as is. The problem, Byrd cautioned against submission to a "razzle-dazzle selling job."

he said, will be to fend off "killer amendments" that would make it unacceptable to either the Reagan administration or the Soviet Union.

In announcing the committee's schedule, Foreign Relations Committee Chairman Claiborne Pell (D-R.I.) said hearings on ratification of the treaty would begin with testimony Jan. 19 from Secretary of State George P. Shultz and Defense Secretary Frank C. Carlucci and continue for about a month. About 40 witnesses will be called, and a panel of European parliamentarians will be consulted, according to committee sources.

The Armed Services Committee and the Select Committee on Intelligence will conduct separate inquiries on issues within their jurisdictions and report back to Foreign Relations in time for final committee action in late February, Pell said.

In addition to all negotiating documents, which Senate leaders have requested and Shultz has said he would deliver, Pell said he has asked the administration to prepare a "legal analysis covering the full scope and precise content" of all obligations and understandings that developed during the bargaining.

The request is apparently aimed at heading off the kind of bitter dispute over treaty interpretation that arose earlier this year in connection with interpretation of the 1972 Antiballistic Missile (ABM) Treaty and its implications for development of Reagan's Strategic Defense Initiative (SDI). Pell said negotiating documents not provided to Congress in connection with the review would have "no legal relevance" as far as the Senate is concerned.

Byrd has set no date for floor action on the pact, stressing a need for "caution and thoroughness." A Senate vote by Easter would be possible although such prompt action is considered unlikely.