Officals from 33 nations, including U.S. Secretary of State Cyrus Vance and Soviet Foreign Minister Andrei Gromyko, signed a convention today banning environmental war.

Signing the converation, a joints U.S. Soviet initiative last year at the Disarmament Conference came just before the opening of talks between Vance and Gromyko that are expected to focus on the nuclear arms deadlock and Middle East issues. The two met as heads of delegations to the Strategic Arms Limitation Talks (SALT).

The convention signed today bans "military or other hostile use of envoromental modification techniques having widespread, long-lasting or severe effects."

A U.S. spokeman said after the subsequent SALT session of two hours and 20 minutes that there was "a full exchange of views."

In Washington, President Carter had a 90-minute meeting with key senators on the nuclear negotiations. Senate Republican leader Howard H. Baker Jr. of Tenness said the President "suggested ideas for negotiations that were ventilated an dexamined carefully.

[These suggestions, which participants were not asked to disclose, were said to be within the framework of the U.S. proposals spurned by the Soviets in March. There were bipartisan agreement that the United States should negotiate cautiously in Geneva, with "no deadline,"]

The U.S. spokeman said here that dtoy's talk "had to do with the proposals put forward by both sides" in recent months but added that he did not know of any new proposals by the Soviets.

This raised the possibility that the Soviets are asking about the two earlier Carter adminstration proposals rejected in Moscow.

One called for substantial sutbacks in the number of nuclear-tipped missiles and bombers in each arsenal, plus some restrictions on new U.S. cruise missiles and the Soviet Backfire bomber.

The second proposal called for an agreement based on the higher level of weapons limitation reached at Vladivocstok in 1974, but would set aside settlement on the cruise missile and Backfire problems.

The White House meeting on SALT yesterday, coninciding reflected President Carter's attempt to assure Senate support for any new nuclear accord with the Soviet Union.

This is one of the most critical U.S. issues, for it takes a two-thirds vote in the Senate to ratify an agreement. Obtaining that support may depend on how an accord affects the American deevloped ckuise missiles, which the Soviets seek to limit.

Cruise missiles were "discussed at length" at the White House, Sen. Baker said. Sen. Hubert H. Humphrey(D-Minn.) said cruise missiles are "our ace in the hole," because of the American technological lead.

Sen. Henry M. Jackson (D-Wash.), a champion of cruise missiles, reportedly was given assurance that congressional committee will be informed - of any appreciable change in the U.S. position.