In one of those deligthful ironies that can emerge only in the U.S. Senate, Republicans warned yesterday that they may resort to a filibuster in order to block a further change in the filibuster rule itself.

Republican senators said changes in the rule being proposed by Senate Majority Leader Rober C. Byrd (D-W Va.) might turn it into a "gag rule" that the 62-to-38 Democratic majority could use to bottle up and crush legislative proposals by the Republicans.

Two years ago the Senate, after a bruising fight, reduced the number of votes needed to break a filibuster against a bill from two-thirds of those present to a flat 60 votes.

But since then, James B. Allen (D-Ala.) and others have learned ways to get around the new rule and stall legislation even after the 60-vote majority is obtained to invoke cloture against a filibuster. The technique consists of demanding repeated quorum calls, challenging rulings of the chair and insisting the roll calls be taken, and similar dilatory tactics. Last year Allen used these devices to held up the antitrust bill and a measure authorizing court-appointed fees for civil rights attorneys for weeks. In the past, filibusters were used mainly against civil rights bills; now they are used for anything.

Byrd isn't proposing to reduce the 60 votes needed for cloture, but he wants to block some of the post-cloture dilatory moves. In a delicious turnabout. Allen himself is supporting the Bird porposals in order to ward off even more drastic revisions.

On the other hand, Jacob E. Javits (R-N.Y.) a leader in numerous fights to ease the filibuster rule, said the Republicans are now a "small minority" and "I'm not for throtting a minority."

Minority Leader Howard H. Baker Jr. (R-Tenn.) said Republicans are "not yet" in an all-out filibuster, but left little doubt they soon may be, unless the Byrd proposal is watered down.

Under existing rules, after 60 votes are obtained for debate-limiting cloture, each senator may have one hour to speak. But there is nothing to prevent him from demanding quorum calls repeatedly in order to obtain further delay. The time for these quorum calls and other procedural stalling devices isn't counted against the maximum of 100 hours allowed for post-cloture debate.

The Byrd proposal would reduce the overall time for consideration of a bill, once cloture is invoked, to 50 hours (one haIf hour Per senator). It would also stipulate that quorum calls and other time-consuming roll calls and procedural motions be taken out of the 50 hours. (The 50 hours could be reduced still further by a two-third vote later.) And when the 50 hours were up the Senate would proceed to a final vote even if all qualified amendments hadn't been disposed of.

Republicans claim dhtat this would mean that any time used up on procedural votes would reduce the time left for speaking and amending, so that everyone wouldn't really be guaranteed a half-hour, and that the majority could "sweep away" amendments they didn't like by blocking their being called up before the 50 hours was over.

Byrd also proposed these other rules changes applicable both in filibuster situations and at other times: (1) Reading of a conference report (sometimes hundreds of pages long) could be dispensed with by simple majority vote, without debate, if a written copy were available, instead of requiring unanimous consent, (2) Reading of the Senate Journal could be dispended with by majority vote without debate instead of requiring unanimous consent (3) The presiding officer's ruling that a quorum is present would be final if a roll-call or a quorum call had just finished and there had not been any intervening business.

Nobody knows how long debate on the rules changes will last if Republican dig in and no compromise can be reached. Republicans will causes to plot their strategy today.