Sen. John Glenn (D-Ohio), an increasingly important figure in the debate over a new strategic arms limitation treaty (SALT), said yesterday that the Carter administration's assurances last week that the pact will be verifiable left him unconvinced.

Glenn said he "absolutely" will not vote to approve the proposed agreement until he is assured that Soviet weapons tests can be adequately monitored for compliance with treaty limitations. He recommended that President Carter delay signing a treaty until the administration has "a better handle on where they are going to get that verification."

"The Senate is not going to buy an unverifiable treaty," he said on "Face the Nation" (CBS, WDVM). "We're not just going to accept on faith that they [the Soviets] are going to live up to it."

Verification, Glenn said, will be "the critical issue" in the Senate, especially with the loss of U.S. monitoring stations in Iran.

The administration has been making a concerted effort to persuade skeptics in the Senate that it is sensitive to the problems of verifying Soviet compliance with SALT.

Last week, following reports that CIA Director Stansfield Turner estimated that it would take five years to make up completely for the loss of the intelligence-gathering assets in Iran, Defense Secretary Harold Brown issued a formal statement saying that adequate verification could be achieved in "about a year."

Brown said the United States can "expect to conclude a treaty that resolves satisfactorily the remaining provisions on verification. . . . In that event, it is my judgement that our monitoring will be such as to provide adequate verification as to Soviet compliance with the [treaty's] curbs on new or modified ICBMs," or intercontinental ballistic missiles.

Asked yesterday if Brown's statement was persuasive, Glenn said flatly, "No." He said Brown has yet to point out how this verification will take place, adding, "We want to see the fine print."

"The implications of turning down SALT are tremendous, but we're not going to buy a pig in a poke. Nobody is."

With 20 or 30 senators against the treaty in principle, Glenn estimated that failure to assure the others on the verification issue would doom approval.

Treaty approval requires a two-thirds vote of those senators present and voting.

Completion of the treaty has been described as "imminent" for months. In the meantime, Glenn is one in a parade of senators-liberals as well as moderates-who in recent months have raised questions about approving it despite a natural inclination to do so.

Some liberals, such as Sen. George McGovern (D-S.D.), have said the treaty does not go far enough to limit the nuclear arms race.

Some conservative politicians think it allows the Soviet Union too much progress in weapons development. John Connally, a Republican presidential candidate, took that position on the television show "Issues and Answers" (ABC, WJLA) yesterday.

"The Soviets are going to achieve much more under SALT II than we are," he said, "and this is not in our best interest. . . . What little I've seen of it [the treaty proposal], I think it's going to permit the Soviets frankly to achieve nuclear superiority between now and 1985."

Connally yesterday came out for a 10 percent increase in the defense budget-independent of SALT-so the United States could build the B1 bomber and a nuclear aircraft carrier, and speed up deployment of the MX missile.

All other agencies would absorb 5 percent budget cuts in a Connally administration, the Republican candidate said, and American taxpayers would be granted a 15 to 20 percent tax cut.

The cuts, he said, would not necessarily reduce social spending. He would concentrate on "fraud" and "waste" instead. CAPTION: Picture, Sen. Glenn: "not going to buy a pig in a poke" AP