Senate Democrats tucked a little Christmas present away for their party shortly before recessing for the holidays, a gift they believe will make them look tough on defense during election-year 1982.

"One of the most delightful and strategic tactics I have seen on the floor in a long time," said Majority Whip Ted Stevens (R-Alaska) as he sensed what the Democrats were trying to do in the midst of debate on the Pentagon appropriations bill.

By the time the Senate had finished the debate, Republicans had been forced to vote against amendments making America's military forces more ready to fight.

This sets the stage for the Democrats to hurl back at the Republicans in 1982 the same political grenades on "military readiness" that exploded around President Carter and his allies in 1980.

"They'll have a hard time explaining away their votes against readiness," chortled one Democrat who played a leading role in offering the amendments.

The Democrats planned their amendment strategy in the office of Minority Leader Robert C. Byrd (D-W.Va.) on Nov. 30, hours before President Reagan's record-high defense appropriations budget was to come up for floor debate.

Byrd advised senators who wanted to try to kill Reagan's B1 bomber and MX missile-basing scheme to lead off the debate with amendments to upgrade military readiness, and save their proposed cuts for last.

After the meeting, Sens. J. James Exon (Neb.), John Glenn (Ohio), Ernest F. Hollings (S.C.), Carl Levin (Mich.), Sam Nunn (Ga.) and David H. Pryor (Ark.) divvied up the readiness amendments to be offered.

As Stevens, chairman of the Senate defense appropriations subcommittee that hammered out the military money bill, saw Democratic strategy unfolding on the floor, he warned his Republican colleagues what they were up against. Referring to the first of the amendments, offered by Levin to restore money to build eight KC10 flying tankers, Stevens said:

"They are good tactics. I hold no malice for my good friend from Michigan. He is going to put me in the position of voting against the KC10s, and I do favor, ultimately, the construction of all eight."

But Stevens said the defense bill could not hold any more additions and he urged his colleagues to join him in voting it down.

The Republicans stuck with him, with not one voting for the Democrats' readiness amendments. But in doing so, the Republicans made a record of voting against the kind of military actions they had demanded during the 1980 election campaign. Examples:

A Levin amendment to add $222 million to buy four KC10 combination tanker and cargo planes to help the services reach distant trouble-spots was defeated, 55 to 38, with only five Democrats joining the 50 Republicans on the winning side.

A proposal by Hollings to add 6,000 people to the Army and 6,000 to the Air Force to help handle broadened commitments was rejected, 54 to 36, with four Democrats joining 50 Republicans.

Another Hollings amendment, to buy the Army $148 million more in ammunition, was killed, 55 to 36, with five Democrats joining 50 Republicans.

An Exon amendment to add $60 million to speed shipment of tanks and other weaponry from factories to troops in the field, was defeated, 56 to 37, with six Democrats joining the 50 Republicans.

A Glenn proposal to add $74.6 million to keep two aircraft carriers operating in the Indian Ocean to cover Persian Gulf trouble-spots, was rejected, 56 to 40, with seven Democrats joining 49 Republicans.

After those amendments were voted on, with Democrats filling the Congressional Record with plenty of material for future political speeches, Hollings proposed killing the B1 bomber. He contended it will be obsolete for penetrating the Soviet Union shortly after it is built and that the $2.4 billion that could be saved by canceling it could be invested in conventional forces.

As anticipated, the B1 survived easily as Hollings was defeated, 66 to 28. Similarly, Reagan's MX basing scheme came through the Senate debate only dented, not demolished.

But Democrats emerged from the debate feeling they had discovered a way to take on Reagan's super-weapons without looking soft on defense: accentuate the positive side of cancellation by showing how the money saved would buy more bang for the taxpayer's buck by going into other military projects.