* S&P delays publishing Romania rating outlook in unusual decision * Leu near four-week highs, Romanian stocks outperform region * Zloty gains beyond 4.3/euro for first time in weeks * Polish central bank meeting seen assessing public spending plan (Adds Romanian government bond auction and government letter on changes in tax plans, OTP Bank shares rise to record high) By Sandor Peto BUDAPEST, March 4 (Reuters) - Romanian assets gained on Monday after an unusual decision by Standard & Poor's not to deliver a rating outlook, raising hopes for changes in a widely criticised bank tax.
The government sharply increased its offer at an auction of 2021-expiry bonds, still selling them at an average yield of 3.8 percent, 24 basis points lower than four weeks ago.
S&P affirmed Romania's 'BBB-/A-3' ratings on Friday. But instead of changing its outlook to negative from stable, as some had expected, the agency delayed its decision for two weeks, at the request of the government.
That fuelled hopes for changes in the bank tax. Finance Minister Eugen Teodorovici said on Wednesday the tax might exempt several financial assets.
New taxes imposed this year are painful for banks and, being linked to the ROBOR interbank rates, complicate monetary policy.
Romania could escape a downgrade of its rating outlook if it disconnects the tax from ROBOR and exempts government bond holdings from the tax, Raiffeisen analyst Stephan Imre said in a note.
A letter to S&P from the government, released by an opposition lawmaker, pledged to make the tax a fixed rate and could exempt treasuries and government-backed credit lines.
The yield on 10-year Romanian government bonds was bid 12 basis points lower at 4.86 percent, after a jump on Friday ahead of the S&P rating review.
The yield remains well above Poland's 10-year bond yield, which dropped by 2 basis points to 2.864 percent.
"We see nominal yield levels to remain high in Romania in the absence of more policy clarity," Erste analysts said in a note.
The leu approached four-week highs beyond 4.732 versus the euro. It traded at 4.7405 at 1407 GMT, up 0.1 percent.
Bucharest's main stock index outperformed regional peers, rising 1.5 percent. Lender Banca Transilvania gained 4.5 percent.
Warsaw stocks were steady, while the zloty firmed about 0.1 percent, to trade at 4.2995 versus the euro. It broke 4.3 for the first time since early February.
Data showing low inflation and slowing growth knocked the zloty to its lowest in more than three months at 4.3455 last month from 18-month highs set at 4.2555 on Jan. 31.
The Polish central bank will hold its first meeting on Wednesday where it can look at a government plan to boost spending.
"Monetary Policy Council meeting ... shouldn't bring any change ... especially since the possibility of interest rate cuts vanished after last week's announcement of government fiscal easing," Millennium Bank said in a note.
Elsewhere, the stocks of Budapest-based OTP Bank, which reported record profits for 2018 on Friday, hit record highs, rising more than 1 percent.
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