Senate Democratic leaders have agreed to the first phase of a strategy to minimize the possibility that crippling amendments will be added to the U.S.-Soviet Intermediate-Range Nuclear Forces (INF) Treaty as the Senate moves toward ratification of the pact this spring.

Under a "consensus" reached last week by Majority Leader Robert C. Byrd (D-W.Va.) and key Democrats, the Senate Foreign Relations Committee will attach no more than one condition to the treaty when it reports the pact to the Senate floor in late April or early May, according to Democratic sources.

Still under review is whether that condition -- which involves the controversial issue of the Senate's treaty-making powers -- will be considered in committee or on the Senate floor, the sources said.

The strategy so far does not rule out considering other provisos on the Senate floor. But it would block what one Democratic leadership aide called a "salad bar" approach to consideration of potentially crippling amendments, reservations or other conditions that could force renegotiation of the treaty.

It would also block treaty critics such as Sen. Jesse Helms (R-N.C.), ranking Republican on the Foreign Relations Committee, from using the committee as a platform for launching "killer" amendments that could doom the treaty by forcing renegotiation of critical provisions.

The move to limit amendments in the Foreign Relations Committee has at least tentative backing from senior Democrats on the panel, as well as the support of Byrd, Armed Services Committee Chairman Sam Nunn (D-Ga.) and Sen. David L. Boren (D-Okla.), chairman of the Select Committee on Intelligence, according to Democratic leadership sources.

The sources said Byrd, Nunn, Boren and Foreign Relations Committee Chairman Claiborne Pell (D-R.I.) agreed on the strategy while traveling to and from the White House last week for a report on their NATO fact-finding trip last month.

The agreement envisions action -- either in committee or on the Senate floor -- to add language along lines proposed earlier by Sen. Joseph R. Biden Jr. (D-Del.) to bar any future reinterpretation of the treaty without consent of the Senate.

Conservative Republicans have voiced opposition to such a move on grounds it could undercut the Reagan administration's attempts to reinterpret the 1972 Antiballistic Missile Treaty to permit advanced testing of its space-based Strategic Defense Initiative.

But the move has wide support among Democrats, including Nunn, who favors a move to augment assurances from Secretary of State George P. Shultz that administration testimony on the INF pact would be the authoritative interpretation of the pact.

The treaty, signed by the president and Soviet leader Mikhail Gorbachev at the Washington summit in December, would eliminate land-based missiles with a range of about 300 to 3,500 miles.

Biden, who underwent surgery last month to correct an aneurysm and faces surgery to correct a smaller one in a few weeks, may miss most or all of the INF debate, according to aides. But Democratic colleagues have said they will offer his treaty-interpretation proposal either in committee or on the floor.

Byrd is reportedly leaning toward taking up the proposal on the Senate floor, while Democrats on the Foreign Relations Committee are pushing to have it handled in committee.

The treaty-interpretation proviso could be harder to remove if it is included by the committee in the resolution of ratification. But Byrd reportedly believes it could be easier to avoid a serious partisan split on the issue if it is handled on the floor.

While the Biden proposal could encounter some strong Republican opposition, Democrats say they believe they have the votes to get it approved without jeopardizing approval of the treaty. Some have indicated, however, that they will drop the proposal if it threatens the treaty itself.

Reservations may be approved by majority vote, although a resolution of ratification for the treaty needs a two-thirds vote for approval.

Democratic leaders have said they anticipate no more than 15 votes against the treaty and believe they have a majority vote to block any crippling amendments as well as the 60 votes necessary to break any filibuster that might develop.

The decision to limit consideration of amendments in the Foreign Relations Committee casts doubt on the fate of several other Biden proposals, including one to impose interim restraints on deployment of long-range strategic weapons pending negotiation of a treaty to reduce those weapons.

The schedule for action on the treaty has slipped by several weeks, largely because time taken for consideration of its terms, including testimony to determine an "authoritative" interpretation by the administration, has been longer than anticipated.

Action by the Foreign Relations Committee, once anticipated by early March, is scheduled to begin during the week starting March 21. The Armed Services and Intelligence committees are planning to report their findings to the Foreign Relations panel during the preceding week. A final appearance by Shultz is also possible but not certain during that week, committee aides said.