Poland gained an inch today on its financial tightrope but still has yards to go after signing an agreement with Western banks to reschedule the $2.4 billion it owed last year.

Still very much in question is the deal the Warsaw government will be able to negotiate with Western banks, and particularly Western governments wary of granting concessions to the martial-law government, to postpone payment of the $10 billion due this year.

In a closed-door ceremony in Frankfurt at the Dresdner Bank, Marion Minkiewicz of Poland's Bank Handlowy, with Poland's Deputy Finance Minister Witold Bien, signed the rescheduling agreement with officials from 20 Western banks. The Western banks at the signing made up the international task force representing the more than 500 banks with outstanding Polish debts.

The agreement provides that repayment of 95 percent of the principal due last year will be suspended for four years, and then paid back over seven years with equal, semiannual installments. The remaining 5 percent will be due in three installments this year.

The signing took place nearly four months later than originally planned because of Poland's inability to repay until last month the $500 million in interest outstanding last year.

With fresh Western financing so far denied them as a result of the Dec. 13 crackdown, the Poles have been unable even to begin making payments on the interest and principal due this year.

Polish officials have argued that without new credits, their country stands little chance of covering past debts. But the rescheduling process, which involves 16 Western governments in addition to the banks, has been halted by the West's condition that future negotiations depend on an end to martial law in Poland, release of those detained and a resumption of talks between Communist officials and the suspended independent trade union Solidarity.

At a meeting March 18 of the so-called Paris Club--an ad hoc gathering of official creditors of a country whose debts are being rescheduled--a written Polish request to begin new talks was rejected on grounds that little had changed in Poland, according to diplomatic sources in Paris.

Without a lead from the governments, the banks lack a basis to reach new terms with Poland. They have made clear that new loans will be conditioned on state insurance cover.

Western officials believe the Soviet Union aided Poland in scratching together the money to repay the 1981 debts. Repayment also seems to have been facilitated by an improvement in Poland's coal production under martial-law discipline. Coal is one of the country's main exports and earners of hard Western currency.

The prospect of a return to economic stability in Poland is a key to any future rescheduling plan. So perhaps is some sort of Soviet tie-in. For the moment, however, Western banks and governments appear to be marking time, avoiding a deeper review of the long-term aspects of the problem.