The world's largest, costliest and deadliest submarine was christened here today in a ceremony in which Rosalynn Carter departed from herprepared text to make an impassioned plea for the pending strategic arms limitation treaty (SALT II).

"The people our our country know that it is a choice between controlling nuclear weapons and not controlling nuclear weapons," Mrs. Carter said in adding her voice to the administration's campaign to sell SALT II.

"As sure as I'm standing here today," she said in a voice rising to combat the wind at the christening of the Trident missile submarine built here by the Electric Boat Co., "I can tell you that when Jimmy signs a SALT treaty, it will be in the best interest of our country and it will be a verifiable."

Outside the terminal, more than 3,-000 antinuclear protesters demonstrating against the Trident tried to block the gates, causing some of the more than 12,000 guests to arrive late. More than 200 protesters were arrested and charged with disorderly conduct.

Before Mrs. Carter took the podium, Sen. John Glenn (D-Ohio) delivered the main christening speech on behalf of the first Trident, the USS Ohio. Glenn, in the text of the speech circulated here today and in Washington Friday night, had contended the United States will not be able to verify whether the Soviets are living up to the terms of SALT II.

"With the recent loss of our intelligence-gathering capability in Iran," Glenn said in his prepared text, "very serious doubts have been cast on our ability to verify" SALT II.

To make up for that loss, Glenn said he had suggested to President Carter that the United States "insist" on being allowed to fly planes over the Soviet Union during missile tests there or put monitoring devices on the ground inside the Soviet Union.

Glenn said in his text that SALT II should forbid the Soviets from coding the electronic signals their missiles send back during test firings.

Glenn said he had proposed those safeguards in a meeting with Carter on Monday. But in delivering his speech here, he said he had discussed the verification problems of SALT II with Carter today and had decided on the basis of that conversation to skip over that portion of his speech. Glenn asked reporters to make note of his deletion, even though shortly before he spoke his aides had passed out copies of text without the deletions.

Administration officials at the ceremony were puzzled about why Glenn handed out the full text of his speech after deciding against delivering the controversial remarks about the verification problems with SALT II.

The White House learned what Glenn was planning to say when a press release on the speech was circulated by Glenn's office Firday night.

Hurried consulations among senior officials and Mrs. Carter ensued, and it was decided that she should be prepared to respond to Glenn's statements on verification.

She went ahead with the planned response today even though Glenn dropped most of the reference to verification of SALT from his speech. The First Lady said, "It is my feeling, and Sen. Glenn understands this, that premature public debate on issues such as this can be very damaging.

"There are some matters pertaining to verifying the treaty that can't be talked about," she said. "They're too sensitive."

She predicted that when the president signs a SALT pact "it will have your support and the support of the senator from Ohio."

The Carter administration has been counting on Glenn to help win Senate approval of a SALT II agreement, which the senator said will not get the required two-thirds Senate vote "without strong verification" provisions.

Administration officials in Washington said privately that there is no real prospect of glenn's recommended changes in the new SALT pact being sought at this stage in the negotiations. (A Soviet-American meeting in Washington today brought the two countries very close to final agreement, U.S. sources said.)

If Glenn sticks to his latest position on verification of SALT, he probably would end up in the ranks of the treaty's Senate opponents. This would be a blow to the administrations's hope of winning two-thirds approval.

A further dampener on the ceremony came from the protesters outside the gates.

"Mourn the launch of the first Trident," read a flyer passed out by some protesters. Demonstrators said the Trident represents a further escalation of the arms race.

The trident class of submarines will replace the aging fleet of Polaris and Poseidon boats now carrying nuclear missiles around the depths of the world's oceans.

However, the first Trident, the USS Ohio, is a long way from being ready for sea duty. Electric Boat is not expected to deliver it to the Navy until November 1980.

Originally, the Navy expected to have the first Trident by December 1977 and to build three of the giant submarines every year at a cost of about $800 million each. The Navy's latest cost estimate for the first Trident is almost double that, $1.5 billion counting the 24 missiles, which cost $10 million each.

Despite the delays and cost over runs on the huge Trident - the submarine is 560 feet long, about 5 feet longer than the Washington Monument is high - the Navy has no other alternative to the aging fleet of Polaris and Poseidon boats. So it plans to keep building Tridents at the rate of 1 1/2 a year.

Mrs. Carter, in the concluding ceremony here today, welded her initials in the keel of the fourth Trident submarine, to be christened Georgia. She quoted President Carter as declaring last week that "if there ever has been any single one weapon system that has ensured our nation's integrity and security, it has been the nuclear submarines with a strategic weapon capability."

The Tridient I missile that will go in both the Poseidon boats and the new Tridents can carry a load of warheads 6,000 miles compared to 3,000 miles for the Poseidon missile.

The Navy also is working on a more powerful and more accurate Trident I missile that could blow up Soviet missile silos. Critics contend that producing it, a decision the administration has not yet made, would destabilize the nuclear balance between the United States and the Soviet Union. They argue that Trident II would change the U.S. submarine fleet from a second-strike retaliatory force to one armed for a first strike against Soviet weaponry.

Navy submarines contend that if the United States does not intend to deploy the Trident II missile, the Navy could settle for a new missile submarine smaller and less expensive than the Trident. The Navy has just completed a secret study on alternatives to such giant submarines as the Trident and 688-class attack submarines that do not carry missiles.

The christening of the first Trident thus comes as the Navy and Congress are moving toward a reappraisal of what kind of submarines are needed to carry out national nuclear policy in the future.

Navy leaders championing the Trident have stressed that its quietness, greater firepower (24 missiles instead of the 16 on the Polaris and Poseidon boats) and longer range will keep the United States seabase deterrent well ahead of Soviet efforts to neutralize it. With Trident, according to one Navy estimate, the United States would have 10 times as much ocean from which to fire on Moscow as is the case with the present fleet of missile subs.

Adm. Hyman G. Rickover, director of Navy nuclear propulsion, in introducing Mrs. Carter and Annie Glenn, who christened the Ohio here today, said that "the Ohio is the first of a new class of nuclear-powered ballistic missile submarines, which will enable the United States to maintain a viable strategic deterrent."

The 80-year-old Rickover, who participated in the launch of the first nuclear-powered missile submarine at this shipyard in the company of President Truman 27 years ago as Mrs. Carter watched, stood out from the glittering Navy brass on the platform today because of his civilian dark blue suit. Jimmy Carter was assigned to a submarine berth here during that 1952 ceremany. CAPTION: Pictures 1 and 2, First Lady Rosalynn Carter welds her initials into the keel of the USS Georgia, as demonstrators block Groton, Conn., streets a short distance away. UPI