SPRINGFIELD, Mass.--President Reagan said yesterday he was "very concerned" that the Senate may not ratify the pending U.S.-Soviet arms control treaty before he goes to Moscow for summit talks with Soviet leader Mikhail S. Gorbachev.

"I think it would be very upsetting and would put a strain on the summit if the Senate has not ratified the treaty by the time we go there," the president said during a question-and-answer session after his speech to the World Affairs Council of Western Massachusetts.

"We hope and pray that they will, but their scheduling of it has been such that I am very concerned we may have to go without having had it ratified," he said.

Senate Majority Leader Robert C. Byrd (D-W.Va.) said the Senate would not rush to ratify the agreement, though.

"We want a good treaty, that is our objective," Byrd said, telling reporters that the approach of the Moscow summit "doesn't guide me at all," and that "I'm not going to rush to judgment."

The pending treaty, covering intermediate and shorter-range missiles, was signed by Reagan and Gorbachev at their summit meeting in Washington in December.

When the two leaders meet again in Moscow, from May 29 to June 2, one of the issues confronting them will be a treaty still being negotiated on longer-range intercontinental nuclear missiles.

Of this treaty, Reagan said, "There is a great question as to whether it could be ready for signature at the summit."

"We don't want a fast treaty," he said. "We want a good one."

On another issue, the president was asked about a trade bill under consideration on Capitol Hill. Reagan said he would veto it if it reached his desk in its present form.

He also said he would immediately ask Congress to enact a new bill excluding provisions to which the administration objects, such as a requirement that companies give workers notice of plant closings.

In his speech to the group, billed as a scene-setter for the upcoming summit, Reagan proclaimed a "period of realistic engagement" between the United States and the Soviet Union.

"Even while freedom is on the march, Soviet-American relations have taken a dramatic turn, into a period of realistic engagement," Reagan said.

"Two of the most basic rights that we have called on the Soviets to comply with," the president said, "are the right to emigrate and the right to travel. How can we help but doubt a government that mistrusts its own people and holds them against their will?

"And what better way would there be to improve understanding between the United States and the Soviet Union than to permit free and direct contact between our two peoples? In the new spirit of openness, why doesn't the Soviet government issue passports to its citizens? I think this would dramatically improve U.S.-Soviet relations."

On Afghanistan, Reagan told his audience, "Now the Soviets say they have had enough."

"But let me say here that the next few momths will be no time for complacency, no time to sit back and congratulate ourselves. The Soviets have rarely before--and not at all in more than three decades--left a country, once occupied. They have often promised to leave, but rarely in their history, and then only under pressure from the West, have they actually done it."

Later in the forum Reagan told what he conceded was a "very cynical" joke as part of his response to a question about the Middle East at a world affairs forum here.

After pledging efforts to secure talks between Israel and its Arab neighbors, Reagan said:

"I can't resist telling you a little joke. It's kind of cynical--very cynical in a matter of fact--about the Middle East."

In the joke, a scorpion comes to a creek and asks a frog to carry him across it, because scorpions can't swim.

The frog says, "Why, you'd sting me if I did."

The scorpion responds, "That'd be silly because if I stung you and you died, I'd drown."

"Well, that made sense to the frog so he said, 'get on,' and started ferry him across and in midstream the scoprion stung him," the president said.

As both were dying, the frog asked the scorpion, "Why did you do that--now we're both going to die."

"And the scorpion said, 'This is the Middle East,'" the president said.