Mitch Snyder, the radical Christian activist and longtime demonstrator on behalf of Washington's homeless street people, yesterday completed the 57th day of a protest fast against the Navy's decision to name a nuclear-powered submarine the "Corpus Christi," or body of Christ.

Thin and pale, Snyder, 38, lay in a sparsely furnished bedroom on the fourth floor of the communal home at 1345 Euclid St. NW he uses along with fellow members of the Community for Creative Non-Violence.

"Putting the name of God on an instrument of destruction is the ultimate perversion," he said in an interview. " . . . Something is wrong when we start giving our weapons sacred names."

Despite the nearly two-month-long fast, Snyder appeared in stable, although weakened, condition. Doctors specializing in malnutrition and starvation say, however, that a person with average metabolism may enter a critical stage after about 60 days of fasting and die.

Announced last Feb. 24 as an open-ended, water-only fast, Snyder's action is only a part--although a more visible and dramatic part--of increasing pressure by religious groups and some local legislatures throughout the country--including the D.C. City Council--to force the Navy to change the name of the submarine.

Just yesterday, five House members on Capitol Hill introduced a resolution branding Corpus Christi an "inappropriate" name and calling on the Navy to rename the 360-foot attack submarine, which will eventually be fitted with nuclear weapons, and transfer the Corpus Christi name to a "nonlethal" craft, such as a hospital ship.

Navy Secretary John Lehman has repeatedly announced his refusal to rename the ship and formally told Snyder as much in two recent letters. Lehman has said that the submarine was named after the Texas gulf coast city, and, regarding religious implications, that a military deterrent system is consistent with "traditional church teaching."

In a new development, Lehman last week sent Hugh O'Neill, a close friend and a Navy lawyer, to visit Snyder at the CCNV house just off the 14th Street corridor.

Snyder said O'Neill appeared to be seeking a resolution to the matter and "asked if renaming the "Corpus Christi" "the City of Corpus Christi" would be okay."

"I told him, yes, it would. It would secularize the name," Snyder said, and he would be willing to end his fast.

A Navy spokesman said yesterday, however, that O'Neill went to the CCNV house "just to see what the situation was. We're not negotiating with Mitch Snyder . . . , and there's been no proposal to rename the ship the City of Corpus Christi . . . . We're not considering a name change at this time."

Asked if the Navy would risk letting Snyder die, rather than be forced into changing the name, the spokesman said, "That's unanswerable . . . . You're saying, when will the Navy back off and say, we don't agree with this demand but we don't want the guy to die? It's an unanswerable question."

For his part, Snyder is careful to say his action is an "open-ended fast and not a fast to the death . . . . There's a subtle distinction." He said he could see ending his fast if it was due to "God's will" and not his own weakness and fear of death.

Snyder underwent a similar fast in late 1978 in an effort to force a wealthy Roman Catholic Church in Georgetown to divert part of its $400,000 rebuilding fund to the poor and homeless of the city. The church refused, and CCNV members, claiming Snyder was at the point of death, rushed him to Sibley Memorial Hospital, where he recovered.