UNITED NATIONS, OCT. 1 -- The Security Council today began drafting two documents designed to increase pressure on Iran and Iraq to end their seven-year war, according to diplomats engaged in the process.

The first, a new, more detailed set of negotiating instructions for Secretary General Javier Perez de Cuellar to relay to Tehran and Baghdad, contains a timetable for putting into effect the cease-fire resolution adopted unanimously by the council on July 20.

The second is the text of a potential follow-up resolution that would impose sanctions -- such as an arms embargo -- on either belligerent, if it fails to accept the proposed timetable.

Armed with the threat of a second resolution, Perez de Cuellar theoretically would have more leverage in seeking acceptance of the first.

This two-tier process was the strategy agreed here last Friday by the foreign ministers of the council's five permanent members -- Britain, China, France, the Soviet Union and the United States -- at a working lunch with the secretary general.

The drafting process was delayed six days, U.N. officials and diplomats said, to let the monthly presidency of the council rotate to Italy today and avoid the difficulty of working under the presidency of Ghana, the council member closest to Iran.

Italy began consulting today on the two texts with the other 14 council members. That process should continue through Monday.

By then, preliminary drafting of both documents could be completed by the five permanent members. They are expected to provide their joint versions to the other 10 next week. Only after the full council gives its final approval will the proposals go to Iran and Iraq, through their U.N. representatives, diplomats said.

U.S. officials indicated that they are likely to go along with a Soviet proposal, made public last week by Foreign Minister Eduard Shevardnadze, that the U.N. package be made more attractive to Iran.

Iran thus far has insisted that a formal cease-fire can begin only after an international commission determines who started the war, and it has made no commitment to eventual withdrawal to international frontiers, as the July resolution demands. This stand remains unacceptable to Washington and Baghdad, officials said.

Shevardnadze proposed launching the cease-fire concurrently with the commission, which would make its report in a week to 10 days.

U.S. officials said their "understanding" at the five power ministerial meeting was that in return for Washington's willingness to accept these modified terms, China and the Soviet Union would recognize that this offer is Tehran's last chance.

One member of the five-power drafting team confirmed that the ministerial lunch -- the first in U.N. history -- produced "a clear mandate." He said drafting would be difficult because the final offer would have to be far more precise than the first proposal brought to Tehran and Baghdad by the secretary general in mid-September.