Sen. Majority Leader Robert C. Bryd (D-W-Va.) suggested yesterday that the greatest danger facing the Panama Canal treaties is the possibility that "crippling amendments" will be approved in the Senate debate scheduled to begin Wednesday or Thursday.

Bryd said he thought it is possible that amendments would be offered that "appear so attractive on their surface" that a majority of senators will vote for them, even though their passage would force either a new plebiscite on the treaties on Panama or the reopening of negotiations.

However, after saying that this of possible, Bryd reiterated his belief that treaties , with slight modifications, will win two-third's approval in the Senate.

On another subject, Bryd told his regular weekly news conference yesterday that Sen. Henry M. Hackson (D-Wash.) has offered a new compromise to opponents of deregulation of the price of "new" natural gas to try to move energy legislation out of the deadlocked House-Senate conference committee.

Jackson's proposal would allow a steady increase in the price of new gas between now adnd 1985, when the price would be completely decontrolled. The president and Congress would retain the power to reinstate controls if they thought the price rose too high.

This new proposal is the first substantive suggestion since Congress reconvened to resolve the dispute over gas pricing has held up President Carter's entire energy package.

Bryd said it would be studied over the weekend by opponents of deregulation, led by Sen. J. Bennett Johnston Jr. (D-La), and that these senators would reply to the Jackson suggestion early in the weak.

Bryd said his treaties would be endorsed by two-thirds of the Senate was based on a head count of members but he declined to reveal more precisely what his count shows.

"The president would suffer a very grave defeat" fi the treaties are rejected by the Senate, Bryd said. He predicted dire consequences of defeat both for American diplomacy and Carter's cdomestic standing.

The damage defeat would do a U.S. interest abroad "would not be a temporary injury," Bryd said "It would be one that would last."

Asked if the vote on the treaties is "one of the critical issues of the century," Bryd said he thought so. But he quickly added that an energy program is even more important.

Bryd called Carter's fireside chat on the canal treaties "a plus" in the fight for Senate approval and said Carter might have to address the county again on the subject before the debate is finished.