The Antelope, a 165-foot U.S. Navy patrol gunboat once used in the Vietnam War, yesterday floated near Pier 4 in Southwest Washington as it began its mission as a peacetime, scientific survey vessel for the Environmental Protection Agency.

The EPA recently acquired the $14 million vessel and extensively converted its Navy configuration. Where once there were missile launchers, there now is deck-mounted sampling equipment.

In its war glory, the ship was armed with a three-inch, 50-caliber, rapid fire mount cannon and twin 50-caliber machine guns.

Now, after $1 million worth of work, the boat is equipped with chemistry and microbiology laboratories, a computer and other scientific instruments. These will be used to conduct survey work at various ocean sites where industrial waste and sewage sludge are dumped.

In 1977 more than 7 million tons of sludge and other waste were dumped into the Atlantic and Pacific oceans and the Gulf of Mexico.

With the Antelope's help, the EPA plans to determine how ocean dumping affects the environment, and by 1981 to compile information that will enable it to cut dumping by 5 million tons.

"Keeping people healthy in times of peace is pretty good use for a warship," said EPA Deputy Administrator Barbara Blum. She and other EPA officials toured the boat yesterday.

"The global community has just indiscriminately used the ocean" for its dumping grounds, Blum said. "Now, with this (the Antelope), we can determine the safe locations to deposit waste" and clean up "these garbage cans" of the world, she said.

The Antelope has an initial three-year mission to survey ocean disposal sites and acquire data for the EPA's environmental impact statements.

The statements will then be reviewed by the Council on Environmental Quality to determine what sites should be shut down.

The Antelope, berthed at Pier 4, near Sixth and Water Street SW, will be open to the public today and tomorrow from 10 a.m. to 2 p.m.