In the interest of ecology, Del. Leo E. Green (D-Prince George's) popped open a couple cans of Coor's beer this morning and passed them around the table, where members of the House Environmental Matters Committee promptly drank the contents.

Green's purposes was to demonstrate the effectiveness and safety of a beverage can on which the pull-top, which he wants to ban, has been replaced by push-in holes where the metal remains attached to the inside of the can.

The beer apparently passed the taste test, n but the can may not have.

A parade of opponents said Green's proposal to outlaw flip-top cans after July 1, 1979, would lead to widespread unemployment to Maryland factory workers by employers who would have to choose between moving their plants or making costly changes in their production lines.

The state chamber of commerce lobbyist said the bill "makes no sense." The soft drink association said "neither the state of the art nor the source of supply" is available to comply. A steelworker's union representative said it would cause a direct loss of 1,050 jobs. The brewers association said the punch-in top is "notable only for cutting you." And the licensed beverage association spokesman said Maryland cannot afford to be a guinea pig." He suggested putting Green's bill "in the litter basket."

But Green said the beverage container industry can produce alternatives to pull-tops if it is forced to.

In Vermont, for example, where pull-tops are outlawed, Coca-Cola uses a push-in top similar to the Coor's cans.

Green said the greatest danger of pull-top cans is that the several metal rings can be swallowed by infants and mentally retarded persons. He cited an article in the Journal of the American Medical Association that detailed seven instances of harm resulting from ingestion of the rings.

Ellis Yochelson, a Bowie geologist, said in a survey of 19 Maryland hospitals he found several instances of ingestion of pull tabs.

"You are playing with a loaded gun," said Yochelson.

Green also testified in behalf of another of his bills; one that would permit only beverages in returnable containers to be sold on state-owned property. Nonreturnable bottles and cans account for up to 30 per cent of roadside litter, Green said.

That figure was challenged by James J. Doyle, whorepresented the glass container industry at the hearing. He pegged the figure at no more than 15 per cent. He also disputed Green's argument that charging deposits on bottles and cans would reduce solid waste.

"The clincher," said Doyle, was an experiment in New York City where Pepsi Cola sold 14 million returnable bottles and reported that one year later, 11 million were unreturned. Despite the deposits, "returnables are not returned," Doyle said.

Another form of highway litter is the target of a bill that was the subject of another hearing today before the Environmental Matters Committee.

Sponsored by Del. Charles A. Docter (D-Montgomery), it would require trucks carrying loose materials to be covered by canvas or a similar material.

Doctor said, motorists pay "a lot in insurance premiums" to cover the costs of windshields broken by stones and other material that flies off the rear of uncovered trucks. In Michigan, which recently enacted similar legislation, the damage was estimated at $11 million annually, Docter said.

Del. Raymond A. Dypski (D-Baltimore), a cosponsor, said fertilizer blew off a truck he followed through the Baltimore Harbor Tunnel recently, forcing him to come to a nearby complete stop.

While spokesman for state and local police departments spoke in favor of the bill, representatives of the powerful trucking lobby, which have defeated similar bills for the last 16 years, argued that existing laws are adequate. The state now requires that loose loads cannot come within 6 inches of the sides of the truck.

Albert J. Mascaro, executive vice president of the Maryland Motor Truck Association, suggested that many windshields are broken by stones that are thrown back by truck wheels, which is considered "an act of God" by state law.

Mascaro said buying covers, at a cost of about $200 a truck, would result in higher costs to the taxpayers by forcing contractors to make higher bids on public projects.

The proposal also would work a hardship on older drivers, who might be forced to climb onto their trucks as often as 20 times a day to cover loads, another trucker spokesman said.

On the Senate floor today, a bill to grant immunity power to legislative investigative committees was defeated by a vote of 26 to 17. The bill would have allowed such committees to give "use immunity" to witnesses in order to compel them to testify.

Baltimore City politics, not Watergate, prompted the proposal. In 1975 the Senate Constitutional and Public Law Committee held a year-round investigation into surveillance activities by the city police force. An exhaustive report was issued but the investigation itself was "botched," as one committee member said, because too many witnesses refused to testify.

Opponents charged that it would set "a very dangerous precedent" to give this power to legislative committees when professional state law enforcers, like state's attorneys, do not have such powers.

"If you're going to give them this power you might as well give them the authority to take out an appendix," said Sen. John P. Corderman (D-Washington). "This is a part-time legislature made up of citizens who are no more gifted for this than they are to take out an appendix."